Pet

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This article is about tame monsters. For the process of making monsters into pets, see taming.

In NetHack, a pet is any tame monster that accompanies and assists the hero throughout the dungeon. A pet's loyalty to the hero is measured by its tameness, while its desire to retrieve items is measured by its apport—a pet that survives and wins enough fights can sometimes even grow up into a stronger form.

Monsters that can be made into pets range from mundane animals such as housecats, dogs and horses, to exotic and mythical creatures such as centaurs and jabberwocks, and even to undead and other humanoids such as vampires and trolls.

Starting pets

By default, each role that the hero can be played as starts with an appropriate pet: roles that have a set pet type will always start with that pet (i.e. only Knights can start with a pony), while other roles have an equal probability of starting with a kitten or a little dog.

The player can set the pettype option in their configuration file to start the game with a specific pet, or else set it to none to start without one. Players can also set the catname, dogname or horsename options to give the starting pet for their role a name—certain roles have default names for starting pets that will be used if the player does not specify one. A pet's name can be changed at any time using shift + C or shift + N.

The starting pets associated with each role and the names of those pets (if any) are listed in the table below:

Role	Pet	Default name
Barbarian	<random>	Idefix (if little dog)
Caveman	little dog	Slasher
Knight	saddled pony	<none>
Ranger	little dog	Sirius
Samurai	little dog	Hachi
Wizard	kitten	<none>

Taming

In addition to starting pets, many other monsters can be made into pets by taming them through various methods, e.g. throwing certain types of food to domestic animals or employ some magical means of taming. Tame monsters can also be created through various methods, such as activating figurines or carrying eggs. See the article linked above for a full description of taming methods and restrictions on tameable monsters.

Steeds

Certain pets can serve as steeds for the hero if they have the appropriate body type and the hero applies a saddle to them. A steed's tameness is reduced each time a non-Knight hero mounts one, making it imperative to treat them well and keep them fed where possible. See the article linked above for what riding a monster fully entails.

Pet movement

Pets will very generally try to stay close to the hero's position, and a pet with higher speed is usually (but not always) better at keeping up. Carrying food that a pet considers a treat (e.g. tripe rations) will cause them to follow the hero more closely. Applying a tin whistle or a bell can cause pets to seek out the hero and stay close for a certain amount of turns, while a magic whistle will warp them immediately to the hero's side.

All pets will follow the hero when they change levels (e.g. going up and down stairways and through portals) if they are either leashed or adjacent to the hero at the time, and are also not immobile—immobility includes being in the middle of an action such as eating or equipping armor.

Pets can be trained to more reliably drop items near the hero by giving them treats after they drop something, and this willingness to 'fetch' is known as apport.

Pet displacement

A hero that walks onto a pet's square and is not wielding a bloodthirsty weapon (i.e. Stormbringer) has a ⁶⁄₇ chance of 'displacing' it and switching places, which does not occur if the hero is punished, the pet is inside a shop, the pet is immobile, or the pet is a long worm with at least one tail segment. Failing to displace a pet this way causes them to become scared for up to six turns. If the pet cannot move, there is a ¹⁄₆ chance of the hero and pet switching places regardless.

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that the information below is still accurate, then update the page to incorporate it.

It is no longer possible to displace a pet out of a trap, directly onto a trap, into water or into other hazardous terrain. It is also no longer possible to displace a sleeping or paralyzed pet. It may be possible to displace a pet near a trap, causing it to move onto the trap.

Traps

Pets will try to avoid known traps where possible: if leashed, a pet may also "whine" or "whimper" to indicate that a trap is near, even if it has not been formally detected yet. A pet has a ¹⁄₄₀ chance of stepping on a known trap anyway if passing that trap is required to follow the hero.

Cursed items

Pets tend to avoid squares where a cursed item is present, and a message is printed if a pet does enter such a square—said message will give the name of the item on top of the pile if there are multiple items, and this will not necessarily be the cursed item. The message is not displayed if the hero displaces the pet onto that square, or else if the pet wants to eat any food present on the square. Divine minion pets are not bothered by cursed items.

Leashes

Applying a leash to a pet will keep them closer to the hero, though it alters and limits their movement as well: leashed pets can end up stuck around corners depending on where the hero moves. Leashed pets will also move reluctantly over cursed items more often, and will whine if they sense a that a trap is nearby (though they still risk walking into the trap themselves).

Pet diets

Pets are generally the only monsters besides the hero that are concerned about nutrition: a freshly tamed pet's hunger starts out at 1000, and the general diet of a pet depends on its monster type. Eating for pets also functions much differently than it does for the hero: When a pet eats a food item, the item is split from its stack if applicable and eaten completely "at once", rather than being gradually eaten over a span of turn; the pet is instead made immobile for the same amount of time, and generally finishes a meal around the same time as a hero of the same speed would. Pet monsters that are inediate usually do not become hungry, but also cannot have their nutrition or tameness increased by feeding them.

A pet gains more nutrition from eating food than the hero, with the nutrition gain dependent on their physical size and ranging from two times the nutrition for gigantic monsters to eight times the nutrition for tiny monsters. A pet tamed with food will "devour" the food item, taking half as much time as normal to eat it but only gaining ³⁄₄ of the normal nutrition from that meal. Pets do not experience rotten food effects as the hero does, and will avoid eating food that is harmful for them, e.g. they will not eat old corpses, and will not eat corpses or other comestibles that are acidic, poisonous or causes stoning (including the eggs of a cockatrice) without the appropriate resistance property. See the section on diet exceptions below for a concise list of what pets will and will not eat in a given circumstance.

A pet that becomes hungry will reach "starving" status in 500 turns, and a pet that is starving becomes confused and will have their maximum hit points divided by 3 until they have eaten, at which point their maximum HP (but not their current HP) is reset to normal. A hero can get an idea of whether a pet is hungry or not from chatting with them frequently - in many cases (though not all), their vocalizations will change noticeably, e.g. a hungry dog "barks" while an otherwise-content dog "yips".

The following information pertains to an upcoming version (3.7.0). If this version is now released, please verify that the information below is still accurate, then update the page to incorporate it.

Pets can gain resistances and other properties by eating corpses as the hero can.

Ghouls and purple worms will seek out and devour edible corpses even when not tamed.

Preferred foods

Depending on a pet's diet, the food it is willing to eat falls into one of four categories:

• Treats, which can be used to increase the pet's apport
• Good food, which the pet will eat even when not hungry
• Acceptable food, which the pet will eat only if hungry or starving
• Emergency food, which the pet will eat only if starving

The following rules apply to the majority of pets:

Class	Carnivore	Herbivore
Treat	tripe rations items created by the spell of stone to flesh (e.g. meatballs)	apples carrots
Good	meaty corpses eggs	vegan corpses (i.e. from b j F)
Acceptable	"people food"	vegan non-corpse non-"people" comestibles
Emergency	vegan non-corpse non-"people" comestibles	"people food"

"People food" consists of the following items:

• food, cram, C and K-rations
• lembas wafers
• cream pies
• pancakes
• candy bars
• fortune cookies

Omnivorous pets use the highest of the carnivorous and herbivorous rankings of a food item; e.g. apples, carrots, and tripe are all treats to them.

Diet exceptions

The following are exceptions to the normal rules established above:

• Pets will not eat anything that would harm them (e.g. poisonous, acidic, or stoning-inducing) unless they have the appropriate resistance. They will also avoid eating "old" tainted corpses, with the exception of lizard and lichen corpses (which never rot away).
  • Ghouls are technically inediate, but will only eat old corpses and old eggs, and consider the former treats.
• Undead and shapeshifted vampires will never eat cloves of garlic.
• Pets that are not immune to sliming will only consider a glob of green slime if they're starving.
• Bananas are treats to herbivorous and omnivorous apelike creatures.
• Carrots are "treats" for blind monsters, who will eat them to regain their sight even if they are carnivorous.
• Metallivores consider non-rustproof iron items a treat, and other metal items such as tins are acceptable food. A metallivore will not eat an amulet of strangulation or ring of slow digestion.
• Gelatinous cubes consider organic non-food items acceptable.
• Humanoids other than ogres, orcs, and kobolds will not commit cannibalism unless starving. elves will not commit cannibalism even if starving.
• None of the above pet types will ever eat the quest artifact of the hero's role, any unique items, or any Rider corpses, and they have a ¹⁹⁄₂₀ chance of passing up on eating any other artifact if they would normally eat its base item.

Combat

Pets that have non-passive attacks will use them in combat against other monsters. They will attack monsters that are peaceful and hostile to the hero alike, and avoid attacking the hero themselves where possible unless they are confused or under conflict—monsters will retaliate against attacks from other monsters ³⁄₄ of the time, giving pets a slight advantage when attacking other monsters.

Pets that have a breath weapon or spitting attack will use it if there is a monster in its range to attack. Pets that can cast monster spells will only use self-targeting spells, and cannot cast them against other monsters normally: they will only use cure self, haste self and disappear, and will only use the lattermost spell if the hero can currently see invisible.

The following exceptions apply to pets targeting monsters to fight:

• A pet will not attack any monster that is two or more levels higher than them.
• A pet that can see a floating eye will avoid attacking it ⁹⁄₁₀ of the time, even if they have a source of reflection.
• A pet will avoid attacking a gelatinous cube ⁹⁄₁₀ of the time.
• A pet will not attack a monster whose passive attack has maximum damage that exceeds their current hit points.
• A pet will not attack peaceful monsters while the pet is below ¹⁄₄ (25%) of their maximum HP.
• A pet will not attack a peaceful quest leader or quest guardian.
• A pet will not attack a monster who can turn them to stone if the pet does not have stoning resistance.

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that the information below is still accurate, then update the page to incorporate it.

Pets are now more careful about attacking monsters that are higher-level compared to their own level as their own health drops, and a healthy pet can attack monsters that are exactly 2 levels higher. Pets will not attack a monster above a certain level, as described in the table below; as before, they also will not attack peaceful monsters at all if they are below 25% health.

Pet's HP	Maximum level (from 3.7.0)
Full health	Pet's level + 2
At least 80% of maximum	Pet's level + 1
At least 60% of maximum	Pet's level
At least 40% of maximum	Pet's level – 1
At least 20% of maximum	Pet's level – 2
Below 20% of maximum	Pet's level – 3

Pet growth

For more detailed information about a monster's stages of growth, see Growing up.

Pets level up by defeating monsters, and the hero is not considered responsible for any monsters killed by their pets. The process of gaining levels for pets and other monsters is distinct from the hero gaining experience levels: rather than gaining experience points that build towards a new experience level, a pet that kills another monster gains a random number of hit points, with a minimum of one and a maximum equal to the defeated monster's level plus one—their level is increased to roughly match their maximum hit point total, with the limit set at the bottom of the next level (compared to the top for the hero).

The maximum HP threshold per level for most monsters is 8 times their current level (or 4 for level 0), while the threshold for golems is 10 plus their current maximum HP, and the threshold for elementals on their home Elemental Plane is 3 times the normal threshold. The maximum level for a monster is ³⁄₂ of that monster's base level, which will normally be no greater than 49. A pet (or any other monster) that has another monster form as a stage of growth and reaches a high enough level will grow up into that form, which cannot be reversed even if the pet is subjected to level drain (though it is possible to polymorph a pet and have the new form be a previous stage).

A pet's health, level and status can be monitored via a stethoscope or a wand of probing.

Pet abuse

Abusing a pet involves the hero attacking it in any form, even if the hero is confused, stunned or otherwise impaired. A hero killing their pet outright carries a −15 penalty to alignment record and −1 Luck penalty—displacing a pet in a manner that causes its immediate death (i.e., into a trap or pool of water) has a ³⁄₄ chance of applying a −15 penalty and angers the hero's god.

Pet abuse can cause the pet to turn on the hero and become hostile, and can also affect their revival as noted in the next section.

Pet death

If a pet dies, it can be revived from any corpse it leaves behind using a wand of undead turning or the turn undead spell, while a pet killed by stoning can be revived with the stone to flesh spell. Pets that are not nonliving and were wearing an amulet of life saving at the time of their death will be revived by it as normal, and intelligent pets that can use the amulet will put on any that they come across if possible.

Pets that are revived by undead turning are not guaranteed to return tame: if the hero killed the pet themselves or abused it at least three times, it will never revive tame and has only a 1-in-(times abused) chance of being revived as peaceful, while a pet abused at least ten times will always revive as hostile. Otherwise, if the hero did not kill the pet and did not abuse it more than twice, its tameness is set to a random value from zero and its prior tameness, with an equal probability of each possible value; if this new value is zero, the pet will not revive tame, but still has a ¹⁄₂ chance of being peaceful. A pet that remains tame after being revived, or else is re-tamed manually, retains its tameness value and has its nutrition, abuse and apport reset as though it was a brand new pet.

Attempting to sacrifice the corpse of a pet that died while it was tame at an altar will anger that altar's god - doing the same at a cross-aligned altar will also reduce the anger of the hero's own god. The corpse of a pet that went feral or was otherwise untamed prior to dying is treated as a normal corpse. There is no special penalty for abandoning pets, losing track of them or (surprisingly) targeting their species or monster class for genocide—there is also no penalty for eating a pet's corpse, though the normal effects of that corpse still apply, e.g. cannibalism penalties or aggravate monster from eating cat or dog corpses.

The following information pertains to an upcoming version (3.7.0). If this version is now released, please verify that the information below is still accurate, then update the page to incorporate it.

Per commit 31471503, successful prayer while standing on a co-aligned altar with the corpse of a pet on it can revive that pet.

Per commit 3c49cd20, a monster killed by drowning (including a pet) has a normal chance to leave a corpse rather than it being immediately removed—the latter behavior is a holdover from much earlier versions, where it is not normally possible to recover anything from a water square.

Pets and equipment

Though a pet will not keep a "normal" inventory as the hero does, pets that are intelligent monsters will use items such as potions, scrolls and even certain tools if they have a means to (e.g., hands to use potions and wands). Humanoid ones can also wear and replace armor, and monsters that have weapon attacks will hold on to a weapon and wield it to use in combat. As mentioned above, pets will not pick up cursed items, and most will avoid moving onto them where possible. Pets that are vulnerable to silver will always avoid touching silver items.

Weapons and armor

Of the humanoid pets that can wear armor, only medium-sized pets can wear suits of armor and shirts, and only medium or smaller pets will fit into cloaks. Like all monsters, pets know the enchantment of armor and will replace a worn piece of armor with one that gives more AC, regardless of any other properties granted, e.g. they will wear a +3 small shield over a +0 shield of reflection.

Pets with a weapon attack that pick up and wield weapons will replace them according to preference, and must be strong to wield two-handed weapons (listed in italics)—this preference is outlined below, proceeding from highest to lowest:

• any usable artifact weapon (i.e. co-aligned and does not hate their monster type)
• cockatrice or chickatrice corpse
• tsurugi
• runesword
• dwarvish mattock
• two-handed sword
• battle-axe
• katana
• unicorn horn
• crysknife
• trident
• long sword
• elven broadsword
• broadsword
• scimitar
• silver saber
• morning star
• elven short sword
• dwarvish short sword,
• short sword
• orcish short sword
• mace
• axe
• dwarvish spear
• silver spear
• elven spear
• spear
• orcish spear
• flail
• bullwhip
• quarterstaff
• javelin
• aklys
• club
• pick-axe
• rubber hose
• war hammer
• silver dagger
• elven dagger
• dagger
• orcish dagger
• athame
• scalpel
• knife
• worm tooth

Pets can also use projectile weapons for ranged attacks as well. If a monster has a wielded artifact weapon and picks up another one, it can switch to the new artifact and drop the old one if the new artifact is not cross-aligned and the conditions for two-handed weapons are met (if applicable). ("Can" here means the first admissible artifact in the game's internal list of carried objects is chosen.)

Potions, tools and other items

Though a pet will not hold on to most items long-term as described earlier, an intelligent pet with hands can still utilize quaff a potion of healing or extra healing if low on HP, and will throw harmful potions such as acid or sleeping at other monsters.

The unicorn horn and unlocking tools are exceptions to the rule regarding pet inventories: pets will hold on to a unicorn horn to apply if they are afflicted with a status condition, and will also use unlocking tools on locked doors.

Some pets can also put on amulets of life saving or reflection—they have no preference in this regard. A nonliving monster that ends up wearing an amulet of life saving (typically due to being polymorphed from the form they put it on with) will not use up the amulet if they die.

The following information pertains to an upcoming version (3.7.0). If this version is now released, please verify that the information below is still accurate, then update the page to incorporate it.

Monsters can use unlocking tools to open locked chests and large boxes, including pets.

Strategy

From a general outlook, having a tamed monster by your side can serve several useful purposes: they can help kill hostile monsters, detect cursed items, and even aid in stealing from shops without angering the shopkeeper. A pet can also kill a peaceful monster that you want a particular item from, such as a dwarf's pick-axe, without any penalties. Pets can also enlighten newer players to certain aspects of the game, such as which corpses are (mostly) safe to eat and which monsters are safe to attack in melee.

However, pets can also be a hassle to manage: weaker ones that are left to constantly pick fights may eventually end up killed without healing and support from the hero; conversely, if they become strong enough, they will attack peaceful monsters such as aligned priests that you want to keep alive, potentially resulting in either their death or the pet's death. Additionally, unless given stealth in some manner they will wake up nearby monsters (particularly nymphs and leprechauns) that you would rather leave asleep. Pets can also snatch up corpses you were hoping to eat and get in the way of vital spells, wand shots or ranged attacks. The more pets you have, the more tedious it becomes to keep track and the more the above problems multiply, though a magic whistle can alleviate many of them—for enterprising petkeepers looking to ensure that pets stay close to them, this thread from RGRN has some useful advice on how to make sure pets follow you.

One particular "quirk" with regards to pets is the relative weakness of most starting pets—the starting pet has much lower HP than 'wild' monsters of the same type, and not only are falling rock traps and pits enough to immediately kill an unfortunate kitten or little dog, but spectacularly unfortunate players may see them die to a jackal, gecko or even a newt. Players invested in their pet's survival may consider letting them finish off weak monsters like newts and grid bugs to quickly gain levels early on, so that it can become strong enough to survive the traps and encounters in the lower dungeon levels.

An important factor to remember for newer players is that pets only provide clues to non-fatal corpses and noncursed objects. This is generally more relevant to understanding the difference between "not cursed" and "safe to use-test" - the non-cursed helmet your dog walked over with no trouble might be an autocursing dunce cap or helm of opposite alignment.

Feeding pets

Carnivorous pets are easy to feed, to the point that you have to prevent them from stealing most corpses that you want to eat; conversely, herbivorous pets are somewhat trickier to feed due to the relative lack of safe pet-friendly foodstuffs, and are more likely to become confused from hunger as a result. Trees such as the ones found in most maps of Minetown can drop several fruits and vegetarian food items if kicked, though there is the risk of attracting killer bees or (in Minetown's case) angering the Watch; it is also possible to create them by polypiling comestibles.

For horse owners in particular, a common trick usually employed by Knights is to allow the horse to reach starving levels of hunger, then leave the level for a while, and re-enter to toss the now-wild horse a treat, resetting its nutrition and tameness. Non-knights with a horse (or other steed that can be re-tamed this way) can instead opt to mount and dismount their steed repeatedly untill it un-tames.

An inediate pet does not have to eat, but also cannot have its tameness increased with food; this makes inediate pets harder for a hero to keep tame, especially if they or any of the pets step on a level-changing trap. Losing a vampire lord or Archon to a level teleporter is a terrible happenstance, not least because they will potentially turn hostile if not found quickly enough, enabling them to use whatever kit they were given against you.

Caring for pets

As pets are at their most vulnerable during their weaker stages, trap detection is a especially useful skill to hone in order to protect them. Actively leading your pet(s) rather then letting them "lead" you makes it easier to provide a clear path for it, whether or not you use them to detect traps - even stronger pets can be "threatened" by an inopportune trap door if it separates you from them long enough for the pet(s) to become hostile. For other non-relocating traps such as pits and bear traps, you want to #untrap the pet as soon as possible; be warned that unsuccessfully attempting to remove a bear trap will injure your pet, and if done repeatedly may kill it. When untrapping pets, make sure there is a safe square for them to access.

Obtaining telepathy as soon as possible is an ideal goal for most pet owners in order to avoid abusing or killing them while blinded. Telepathy and warning is also ideal to spot and eliminate digesting monsters such as purple worms, trappers and lurkers above, who can potentially engulf and kill your pet instantly. Pets are also vulnerable to polymorph traps, which in practice are as likely to turn them into a sessile mold or jelly as it is to turn them into something stronger.

If you are hallucinating, try using the #chat command to figure out which of the strange beings around you is your pet. A somewhat less reliable option is to wait and see how the creature in question moves and whether or not it attacks you.

Equipment for pets

The best way to equip a pet is to gather the desired items and leave them in a dead end, then stand on them until your pet comes near; swap places with the pet and keep them standing over the pile until they picks up something and start using it. If a pet drops something they had been using, you will need to swap places again to pick up their old stuff. For replacing equipment, the best way to do that is in a 2-square long corridor with a locked door. As pets tend to avoid picking up items when you are nearby, this method may take a while; locking them in a closet will often be faster if you don't have any items to replace. Pets with high apport are more likely to pick up things if you are not within their sight - be sure the pet isn't carrying a key of its own.

If you want your pet to keep a specific artifact, give it to the pet while it is carrying as few objects as possible. A pet that can be armored should be given magic resistance, magic cancellation, and reflection. All items that work for the hero also work for monsters that can wear them, with some notes and exceptions:

• Speed boots make monsters fast, but not very fast—a wand of speed monster or unwanted potion of speed is usually preferable to let them pick up. Spellcasting monsters can use the haste self monster spell to make themselves fast and reapply speed if they lose it.
• An alchemy smock grants only poison resistance.
• Monster spellcasting is not hindered by metal armor.
• Dragon scales and dragon scale mail provide their extrinsics as usual, while other armor properties than those discussed do not affect monsters.

After deciding what extrinsics you can give your pet, the rest of their armor selection should be focused on improving AC.

A user has suggested improving this page or section as follows:

"Expand with tips from this relevant rgrn thread"

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that the information below is still accurate, then update the page to incorporate it.

Per commit 0891ef4e Alchemy smocks grant acid resistance for monsters while worn.

The ability of pets to gain resistances and other properties from corpses makes reflection a less crucial property, although it is still important for pet survival (e.g. against death rays), and puts inediate pets at a relative disadvantage.

Equipment for pet owners

There is a lot of equipment that can make pets more useful or make keeping them close easier:

• Magic whistles will bring all pets to as close to the hero as possible, and blessed eucalyptus leaves act like magic whistles if applied. A tin whistle is a fine substitute if neither is available.
• Stethoscopes will reveal information about your pet, including how injured it is, its level, and its maximum HP. Wands of probing will also give you this information and any equipment the pet is wearing, but they are less efficient due to their limited number of charges.
• Leashes will keep pets nearby.
• Saddles can be used to ride some pets, and Riding gloves and boots will make applying a saddle easier.
• Carried treats will cause pets to stay close to the player; this can be annoying if they're always underfoot.
• Spells of (extra) healing for healing pets, charm monster for acquiring new pets, stone to flesh for making treats for carnivores and omnivores.
• The wand or spell of undead turning and the spell of stone to flesh can revive pets; they may revive hostile.
• The spell of detect monsters and/or potion of monster detection to locate pets.
• The wand of speed monster or potions of speed to make pets fast.
• Potions of healing, extra healing, full healing, restore ability, and gain ability will all restore a monster to full hit points if it hits them (wielded or thrown). Hitting a pet with a wielded potion counts as abuse, however.
• Potions of unholy water will heal 2–12 HP for demons, undead, and lycanthropes.
• A key to lock your pet in a room or closet, so it can heal, or equip itself, or to have it not attack something you want kept alive. Some pets may be smart enough to pick up keys and unlock doors.
• A blindfold or towel if you have telepathy to locate your pets.
• A bag of holding (or a sack) is useful to carry all the other stuff and pet food, keep treats hidden, and to rob shops.
• Crystal balls, including the Orb of Fate and the Orb of Detection, can be used for detecting traps that could harm pets, and can be recharged indefinitely with the Platinum Yendorian Express Card; crystal balls are rather heavy to carry, however.

Preferred pets

Below is a pair of lists detailing monsters that make good pets: the first consists of pets which a player might specifically work to obtain, for example through a wish or a polymorph trap; the second consists of pets that are useful (e.g. if you get them through a polytrap or magic trap), but not usually worth going out of the way to obtain. Pacifist play and speed play may shift a player's priorities, and ultimately this list should not be taken as definitive advice.

A NetHack 3.2.0-era guide by Kevin Hugo gives a quick overview of potential pet candidates with outlined pros and cons.

Worth the effort of trying to obtain

• The Archon is considered by general consensus to be the best all-around pet, with a high maximum level, powerful physical attacks, the ability to heal and haste itself, and a blinding gaze; they can fly, do not eat, and can wield weapons and wear non-torso armor. A "blessed figurine of an Archon" is a common first wish for pacifists, and is popular for pet-keeping heroes in general—wishes are also the most reliable way to obtain one, since Archons cannot be created by polymorph, and they are are rare to find and difficult to tame, owing both to their 80 MR score and highly dangerous attacks. Monsters blinded by an Archon's gaze won't respect Elbereth, which is a possible concern for low-level characters, and they never leave corpses to revive.
• Ki-rin are inediate monsters that can fly, have superb attacks, and are among the best available mounts for aspiring riders: its high magic resistance and base level will prevent it from bucking you if you are generating conflict. They are best for a Knight, as it will always lose one point of tameness each time a non-Knight mounts it. Like Archons, ki-rin are not valid forms for polymorph and never leave corpses.
• Titans have excellent base level, AC and magic resistance, along with high speed, spellcasting, flight, weapon attacks, and the ability to wear non-body armor—they may be the strongest pets obtainable from a polymorph trap. A titan's size prevents them from being engulfed, including by digestion attacks that can instantly kill Archons and ki-rin. Titans are omnivores and will stop to eat corpses, which can be inconvenient but also allows their tameness to be increased, granting a hero more time before they untame if they are left on another level. Titans that are subjected to stoning or else killed without being disintegrated will always leave corpses that can be revived.
• Purple worms have mediocre AC, but their digestion attack allows them to swallow and instantly kill any monster that is small enough and has a low-enough level: a pet worm can be leveled up quickly by setting it loose in a graveyard containing wraiths, since their digestion attack is not subject to corpse generation odds. However, they must be kept away from chameleons, doppelgangers and green slimes which will polymorph them; a ring of protection from shape changers will prevent the former two corpses from transforming them. Note that digested monsters do not leave corpses or corpse-related special death drops such as unicorn horns, and some powerful monsters are too large for them to engulf, requiring assistance in order to prevent them being overwhelmed.
• Balrogs have strong weapon attacks, a high base level, good AC, immunity to death magic, and the ability to wear non-body armor, though they move at a significantly slow 5 speed (or 7 speed if made fast) and are vulnerable to digestion. They are inediate and a valid polymorph form, making them somewhat more practical to acquire than the stronger Archon or ki-rin and somewhat easier to keep nearby.

Nice to have if you get one

• Centaurs can use weapons and some armor, may be saddled and used as a mount, and are easy to keep fed. These are potentially excellent early pets for heroes with a scroll of taming or reliable access to the charm monster spell.
• Cockatrices can petrify many foes. They don't have much HP, however, and their low maximum level will prevent them from attacking tougher monsters. Consider using conflict to force your pet 'trice into combat (and watch your messages to be sure you aren't turning to stone).
• Dragons can fly, can serve as a mount, and have very good attacks. Silver and gray dragons are immune to death rays; the former is also immune to disintegration blasts, while the latter is immune to polymorph traps. Yellow dragons are stoning-resistant. Pet dragons can be obtained by polymorphing yourself and laying eggs; eggs hatch into baby dragons which can grow up to full size.
• Winged gargoyles can fly and also have decent AC and attacks; in addition, they are resistant to stoning and starvation. Winged gargoyles are very hard to get by egg-laying; most winged gargoyle eggs hatch into regular gargoyles, and gargoyles do not grow up to winged gargoyles.
• Jabberwocks have excellent damage potential, a natural 18 speed that can be boosted to 24 when hasted and the ability to fly, and are solid candidates for steeds. They lack resistances, though, and are vulnerable to traps, death rays, disintegration rays, and cockatrices.
• Arch-liches can reach terrifyingly high levels, are always by your side even without the aid of a magic whistle, can heal themselves, and have a powerful freezing touch attack. They are impotent against cold-resistant monsters, however, and may often get in your way. Since they will always teleport to your side, it can be very difficult to prevent them from killing priests and shopkeepers. You cannot tame master- or arch-liches directly, but you can tame a lich or demilich and let it grow up.
• A mastodon has a high maximum level of 30 with a decent 12 speed, and boasts two strong headbutt attacks, making them an enticing steed candidate. Hoewever, their 5 AC is lackluster, and as herbivores, they can be tricky to keep fed.
• Mind flayers do a lot of melee damage with their tentacle attacks, and can clear out monsters from a distance with their psychic blasts, which won't damage you as long as the flayer isn't hostile. A confused pet flayer could be disastrous, however, so make sure it has a unicorn horn. A psychic blast could also wake the Wizard of Yendor before you're ready to deal with him. Their very large number of attacks per turn also make them very weak to passive attacks—keep them away from jellies!
• Minotaurs are fast, hit very hard, and are guaranteed to appear on a maze-type level. They have 0 MR, so a scroll of taming is guaranteed to snare one on the first try (the spell of charm monster is of course dependent on your casting success rate).
• Skeletons don't breathe, don't eat, slow monsters, wield weapons, and will resist cold, sleep, poison, petrification, and wands and fingers of death. They are not randomly generated, but can be found in Orcus-town or produced by a polytrap or by polypiling unihorns.
• Trolls have good physical attacks, and if killed may revive tame. They may also revive hostile, however, so be careful. Make sure your other pets don't eat your former pet's corpse.
• Vampires and vampire lords don't breathe or eat, can fly, can wield all weapons and armor, and will regenerate. They are also immune to death rays. But in 3.6 vampires now spontaneously turn into fog clouds, wolves, and—especially—vampire bats and remain in that form unless defeated in battle. Wolves and vampire bats do eat (and move fast enough to steal corpses from you) but they are nearly useless in battle compared to vampires. You can keep a vampire pet in its true form with a ring of protection from shape changers. In addition, protection from shape changers is necessary to permanently change the form of a vampire or vampire lord - without it, polymorphing them will just result in them taking their vampire bat form, which can change again as normal.

History

The first pet introduced in the lineage of NetHack is the starting little dog that a hero begins play with in Hack for PDP-11, which is based on Jay Fenlason's Hack—the little dog continues to serve as the hero's pet in Hack 1.0, all the way to NetHack 2.3e.

NetHack 3.0.0 introduces the kitten as a monster and a potential starting pet, and also introduces role-specific starting pets. NetHack 3.3.0 introduces the starting pony for Knights.

In NetHack 3.6.0 and previous versions, including variants based on those versions, pets only use their breath weapons when subjected to conflict. NetHack 3.6.1 grants pets the ability to use breath or spit weapons against monsters.

Messages

Hunger

For monster-specific messages that can indicate hunger, such as those for a little dog, kitten, or pony, see that monster's article.

<The pet> is confused from hunger.

Your pet is starving. It becomes confused from hunger, its maximum HP is reduced to 25%, and it has 250 more turns to live.

You feel worried about <your pet>.

As above, but your pet is out of sight.

Death

You hear the rumble of distant thunder...

You killed your pet, with a penalty of −15 to alignment and −1 to luck.

You hear the studio audience applaud!

As above, while hallucinating.

You feel guilty about losing your pet like this.

You displaced your pet in a manner that caused it to drown or die. This has a ³⁄₄ chance of a −15 alignment alignment penalty and an angry god.

You feel sad for a moment.

Your pet starved to death.

<Pet> starves.

As above, while in your sight.

You have a sad feeling for a moment, then it passes.

Your pet died from combat or a trap.

You have a melancholy feeling for a moment, then it passes.

Your pet light or sphere exploded.

You have a peculiarly sad feeling for a moment, then it passes.

Your pet was turned to stone.

You have a sad thought for a moment, then it passes.

Your pet mind flayer or master mind flayer ate the brain of Medusa.

You have a strangely sad feeling for a moment, then it passes.

Your pet clay golem was cancelled by a gremlin.

You have a queasy feeling for a moment, then it passes.

Your pet that had a digestion attack attempted to swallow one of the Riders.

May <pet> rust in peace.

Your pet iron golem was eroded by a rusting attack.

May <pet> rot in peace.

Your pet wood golem was hit by a rotting attack.

May <pet> roast in peace.

Your pet paper or straw golem was hit by fire.

Variants

SLASH'EM

SLASH'EM makes various changes to the pet-keeping system, adding god-granted minions as well as pets that can turn traitor. Pets and other monsters in SLASH'EM that are polymorphed will also eventually return to their normal form upon being killed or after a certain amount of turns, much like the hero does.

GruntHack

In GruntHack, hostile monsters will aggressively seek out your pets to attack them - this makes it much harder to keep early pets in particular alive. GruntHack also uses the same rules for polymorphing non-player monsters as SLASH'EM: polymorphed pets will return to normal form when they die or the polyform expires.

AceHack

AceHack implements ranged combat for pets; however, they currently die much faster than in vanilla, as monsters are more aggressive toward them. (This is planned to be fixed before release.)

dNetHack

dNetHack, notdNetHack and notnotdNetHack implement several changes and improvements for pets, which are detailed in the article linked above. These variants also add a charisma-based limit on the total amount of pets, and a beast mastery skill that can augment a hero's pet-keeping ability.

FIQHack

In FIQHack, pets actively seek out hostile monsters to pursue—applying a tin whistle will temporarily disable this behavior.

Intelligent pets that are not currently immobile will prioritize wearing and using items thrown to them by the hero over most other items, with more recently thrown items ranked above less recent ones.

EvilHack

In EvilHack, there is a charisma-based limit on the amount of pets that a hero can keep. Pets are also capable of casting monster spells in combat.