Growing up is the process in which a monster turns into a larger version of itself (e.g., a kitten turns into a housecat). Monsters grow from killing monsters and gaining levels, from the effects of a potion of gain level, or from wraith corpses.
If a monster kills another monster, its maximum and current HP will both increase. If its maximum hp are increased above the threshold for its current level, it will gain a level. There is a limit to maxhp and levels a monster can gain in this way.
The monster will increase maxhp by d(victim level + 1), but no more than enough to bring it to the minimum for the next level. Current hp will increase by d(increase in maxhp) - 1.
The maximum level attainable via this method is 3/2 of the base level for the current monster type (or the next type if there is a more "grown up" form), but no less than 5 and normally no greater than 49. Player monsters can reach level 30, and monsters which have a minimum level greater than 49 (named demons) have a maximum level of 50. If an increase in maxhp would increase the monster's level above this maximum, its maxhp are reset to the threshold for its current level.
- a dog (currently level 4, maxhp 31) kills a kobold shaman (level 2). Its maxhp can increase by 1-3. If it gains 2-3 maxhp, it will become level 5, with maxhp of 33.
- a large dog (currently level 9, maxhp 70) kills a dwarf king (level 6) and would gain 4 maxhp. Its maxhp do not increase beyond 72.
A user has suggested improving this page or section as follows:
"It would be nice to have a table on a separate page of each monster and its "natural" maximum level and hp"
A monster drinking a potion of gain level or eating a wraith corpse will gain a level and increase its current and maximum hp by d8.
Monsters may exceed their natural level limit in this way, although they may not exceed a hard limit of 49 (50 for named demons). Additionally, pets eating wraith corpses cannot exceed their base level by 15 (but engulfing live wraiths still works). They may subsequently increase their maximum HP to the cap for their new level by killing monsters.
If a monster gains a level so that its current level equals or exceeds the minimum level of its next available form, it will "grow up" into that form. Starting in NetHack 3.6.0, a message to that effect will be given if you can see or detect the monster ("The little dog grows up into a dog" or "The soldier becomes a sergeant"). This can affect its attack, armor class, and possibly other properties.
Growing up does not allow a monster to take a genocided form. If the new form is genocided, the monster dies and does not leave a corpse. Extinct forms are nonetheless allowed.. This will generate the message "As Foo grows up into Foo, s/he <expires/dies>!" if you can see or otherwise detect the monster.
While many players may only ever notice the growth of domestic pets (dogs, cats, and horses), a surprising number of monsters can grow up in this manner. The possible form changes in NetHack 3.4.3 are:
- chickatrice → cockatrice
- hell hound pup → hell hound
- winter wolf cub → winter wolf
- baby gray dragon → gray dragon
- baby silver dragon → silver dragon
- baby shimmering dragon → shimmering dragon (deferred)
- baby red dragon → red dragon
- baby white dragon → white dragon
- baby orange dragon → orange dragon
- baby black dragon → black dragon
- baby blue dragon → blue dragon
- baby green dragon → green dragon
- baby yellow dragon → yellow dragon
- red naga hatchling → red naga
- black naga hatchling → black naga
- golden naga hatchling → golden naga
- guardian naga hatchling → guardian naga
- baby long worm → long worm
- baby purple worm → purple worm
- baby crocodile → crocodile
Orcs and elves:
- orc / hill orc / Mordor orc / Uruk-hai → orc-captain
- elf / Woodland-elf / Green-elf / Grey-elf → elf-lord → elvenking
- kobold → large kobold → kobold lord
- gnome → gnome lord → gnome king
- dwarf → dwarf lord → dwarf king
- ogre → ogre lord → ogre king
- mind flayer → master mind flayer
Soldiers, Kops and watchmen:
- soldier → sergeant → lieutenant → captain
- Keystone Kop → Kop Sergeant → Kop Lieutenant → Kop Kaptain
- watchman → watch captain
Notably, orc shamans, kobold shamans, and gnomish wizards do not change form. Neither do rabid rats nor vampire bats. Also, even though queen bees can lay killer bee eggs, and winged gargoyles can lay gargoyle eggs, such offspring are sterile and will not grow into their parent forms.
Several monsters added in SLASH'EM also are capable of growing up
- pile of killer coins → large pile of killer coins → huge pile of killer coins
- dingo puppy → dingo → large dingo
- larva → maggot → dung worm
- giant tick → giant flea → giant louse
- deep one → deeper one → deepest one
- lamb → sheep
- shoggoth → giant shoggoth
- gnoll → gnoll warrior → gnoll chieftain
- migo drone → migo warrior
- vampire lord → vampire mage
- baby shimmering dragon → shimmering dragon
- baby deep dragon → deep dragon
- gnome lord → gnome warrior (This is a change from vanilla)
In the Convict patch and some other variants that include it, the giant rat grows up into the enormous rat before it becomes the rodent of unusual size. In the latest version of the UnNetHack source code, however, the enormous rat has been removed and giant rats now grow up directly into R.O.U.S.