There are three types of unicorns: white, gray, and black, which correspond to lawful, neutral, and chaotic alignments respectively. Directly killing a unicorn of your own alignment always carries a −5 Luck penalty; eating a unicorn corpse is safe regardless of alignment, and has a 27% chance of giving poison resistance.
Unicorns tend to appear somewhat early in the dungeon, starting around DL 7 or so. Normally generated unicorns matching your alignment will be peaceful; all others will be hostile. Unicorns in bones files or created by polymorph traps may be exceptions to this rule. White unicorns are generated slightly more frequently than the other types; this is to compensate for Gehennom preventing the random generation of lawful monsters.
A unicorn is guaranteed to leave a corpse behind unless killed in a way that destroys it (e.g., disintegration or digestion); it will also leave a unicorn horn with its corpse, unless it has been revived or is a polymorphed monster from a polymorph trap, in which case it has only a 50% chance of leaving one.
Unicorns are extremely fast and can easily outpace even players with very fast speed. A unicorn that can see the player will attempt to avoid being "lined up" by the player (orthogonally or diagonally) even if they are hostile. If a unicorn has no available neighboring square where it would not be lined up, it has a 50% chance of teleporting away each time it tries to move. Attempting to move into melee range of a non-peaceful unicorn will usually cause it to attack you before leaping or teleporting away to an applicable square.
Unicorns do surprising amounts of damage, getting in multiple kicks and butts per turn. However, because they will not intentionally move into melee range, it is usually not difficult to avoid combat with them. This does not apply to pet unicorns that attack monsters, which occurs normally as with any other pet.
In the beginning of the game, when you typically are weak and most need the horn, the most sound strategy for fighting unicorn is to let a pet take it out; this naturally also avoids any Luck penalties for killing a co-aligned unicorn, though the pet may still be killed if the unicorn lands enough counterattacks.
In addition to pets, more combat-capable characters can lead them into hallways and attack with projectiles from a safe distance; rays which bounce from walls are also viable, and a boomerang can be handy in this situation as well. Savvy players can trap it using a pit or a beartrap, though it will only work once per trap; characters at Skilled or better in polearms or lance can pound the unicorn while it is a knight's move away with no fear of counterattacks. Players with very fast speed will have occasional chances to attack with ranged weapons or else close in to attempt direct combat, and a well-armored and prepared very fast player can defeat them fairly easily.
A good way of closing in on a unicorn is to use invisibility: unicorns cannot see invisible, making for a much easier time lining them up to throw weapons or gems at them. However, invisibility can backfire for a weak character - a hostile unicorn that can't see you will not know to stay a knight's move away, resulting in a potential skewering if it closes in. Due to a bug, unicorns are not fooled by displacement while moving to avoid you - once within melee range, however, hostile unicorns will attack as normal and possibly target your displaced image instead of you.
The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.The aforementioned bug is now fixed, and unicorns try to avoid being lined up with where they perceive you to be, even if you are displaced. (commit)
Applying a unicorn horn has a chance of curing blindness, hallucination, confusion, and stunning status effects, making a unicorn horn an essential item for all adventurers - see its article for more details.
Unicorns can use their own horn to cure themselves of these effects, producing the message "The tip of the <color> unicorn's horn glows!" A player polymorphed into a unicorn can use the #monster extended command to do the same, acting as a uncursed unicorn horn would.
Sacrificing a unicorn at an altar is a special case: sacrificing cross-aligned unicorns on your god's altar can reap alignment and Luck benefits, you should sacrifice on your own altar a unicorn of a different alignment. If the corpse, the altar, and you are three different alignments, it is just a regular sacrifice. However, sacrificing coaligned unicorns - or sacrificing any unicorn on an altar of its own alignment - will cause bad things to happen. See the article on sacrifices for more details.
Unicorns and gems
Throwing any gem to any hostile unicorn will make it peaceful. A tamed unicorn will catch and immediately drop gems thrown at it, without any effect on Luck or identification. Unicorns also pick up any gems and stones they come across, worthless or not.
If the gem is worthless glass, a rock, or a gray stone, it will not affect your Luck, and the unicorn will either "graciously" accept it or be "not interested in your junk". If it is valuable, a co-aligned unicorn "gratefully" keeps the gem and improves your Luck, depending on the identification status of the gem: +5 points if the gem is formally identified, +2 points if type-named, and +1 point if completely unknown.
Coaligned unicorns are great for improving Luck and sorting out worthless glass. The game does not check what the gem is named, or what its type is called, as long as one of them is defined - ideally, you should type-name all gems before throwing them at coaligned unicorns. It is easiest to increase Luck this way in a no-teleport level, e.g. Sokoban, in order to prevent them teleporting away after each catch. If you are sure you will not need the unicorn again after, you may want to encourage a pet to kill it so you can recover your gems without any Luck penalty.
A cross-aligned unicorn will "hesitatingly" accept a valuable gem, and your Luck may increase or decrease by one point if the gem is not formally identified, and by up to three points if it is. It is not generally a good idea to throw gems at cross-aligned unicorns unless you're pretty sure they're glass.
- The <color> unicorn's recently regrown horn crumbles to dust.
- A revived unicorn died, but did not drop a unicorn horn.
- The tip of the <color> unicorn's horn glows!
- A unicorn cured a status problem using its horn.
- The <color> unicorn catches and drops the <gem>.
- You threw a gem at a tame unicorn.
- The <color> unicorn is not interested in your junk.
- You threw a formally identified or type-named piece of worthless glass, a rock, or a gray stone at a unicorn.
- The <color> unicorn hesitatingly accepts your gift.
- You threw a valuable gem at a cross-aligned unicorn, and your Luck may have gone up or down.
- The <color> unicorn graciously accepts your gift.
- You threw an unidentified piece of worthless glass or a gray stone at a unicorn.
- The <color> unicorn gratefully accepts your gift.
- You threw a valuable gem at a coaligned unicorn, and your Luck increased by 1, 2, or 5.
- The <color> unicorn catches the <color> gem.
- You threw a (valuable or worthless) gem at a unicorn while blind.
The unicorn is a creature that features prominently in European-styled fairy tales, though it is much older and appears in many other folklores, being depicted as far back as the Indus Valley Civilization in ancient seals, and has been mentioned by the ancient Greeks in accounts of natural history by various writers such as Strabo, Pliny the Younger, and Aelian. In the Middle Ages, depictions of a unicorn trapped by a maiden were an elaborate allegory for the Incarnation of Christ (with the maiden representing the virgin Mary); this likely gave rise to the recurring motif of unicorns appearing to and/or being tameable only by a fair, virgin maiden. Naturally, unicorns are one of many folkloric creatures included in Dungeons & Dragons.
The unicorn is commonly depicted as an equine beast with a single large, pointed, spiraling horn projecting from its forehead; it is quadrupedal and almost always equine or caprine in appearance, with white or light-colored hair. Unicorns are generally nearly impossible to catch, and are fittingly sought after for their various magical properties, such as those inherent to its horn; modern fiction often extends those properties to its other features, such as its hair or blood. "Unicorn" is used as a colloquial term that refers to someone or something that is rare and hard to find.
The Chinese qilin (Chinese: 麒麟), is sometimes called "the Chinese unicorn", and is described as a hybrid animal with the body of a deer, the head of a lion, green scales and a long forwardly-curved horn. The Japanese ki-rin is based on the qilin, but more closely resembles the Western unicorn.
Men have always sought the elusive unicorn, for the single twisted horn which projected from its forehead was thought to be a powerful talisman. It was said that the unicorn had simply to dip the tip of its horn in a muddy pool for the water to become pure. Men also believed that to drink from this horn was a protection against all sickness, and that if the horn was ground to a powder it would act as an antidote to all poisons. Less than 200 years ago in France, the horn of a unicorn was used in a ceremony to test the royal food for poison.
Although only the size of a small horse, the unicorn is a very fierce beast, capable of killing an elephant with a single thrust from its horn. Its fleetness of foot also makes this solitary creature difficult to capture. However, it can be tamed and captured by a maiden. Made gentle by the sight of a virgin, the unicorn can be lured to lay its head in her lap, and in this docile mood, the maiden may secure it with a golden rope.
Martin took a small sip of beer. "Almost ready," he said.
"You hold your beer awfully well."
Tlingel laughed. "A unicorn's horn is a detoxicant. Its possession is a universal remedy. I wait until I reach the warm glow stage, then I use my horn to burn off any excess and keep me right there."
- src/makemon.c in NetHack 3.6.6, line 1271
- src/mon.c in NetHack 3.6.6, line 332
- src/monmove.c in NetHack 3.6.6, line 1089: Unicorns have NOTONL flag set on teleportable levels
- src/monmove.c in NetHack 3.6.6, line 1125: Non-teleportable levels are handled specially, but unicorns still attempt avoidance if possible
- src/mon.c in NetHack 3.6.6, line 1492: Implementation of NOTONL flag behavior in mfndpos()
- src/monmove.c in NetHack 3.6.6, line 1251
- Issue #564: Unicorns ignore player's displacement when avoiding the player
- src/dothrow.c in NetHack 3.6.6, line 1801: function gem_accept()