A polymorph trap changes you to a new species, in the same manner as a polymorph spell, potion or wand. They will not be generated on dungeon levels 1 to 7. The only guaranteed polymorph trap is on the wizard quest locate level.
- If you have polymorph control, you get to choose which monster to become.
- If you are wearing dragon scales or dragon scale mail, you turn into that color dragon. If you were also wearing a cloak, it will be ripped apart (destroyed). Wearing gray dragon scale mail will prevent the polymorph from happening.
- If you have lycanthropy, you switch between your animal and were forms.
- If you are a vampire or vampire bat, you switch between the two.
- Otherwise, you have a (19-Con)/20 chance of suffering a system shock: you sustain d30 damage and abuse your constitution.
If none of the above happened, you either polymorph into a random monster for 500-999 turns, shorter if your polymorphed level is higher than your native level, or if you polymorph into your own race and see: "You feel like a new <race>". This redistributes your attributes and changes your experience level by up to two levels.
This transformation will destroy your shirt, body armor and cloak if you polymorph into something large or bigger, a non-humanoid medium or bigger, or a gargoyle or marilith (wings and extra arms don't fit).
The trap then disappears.
Use by monsters
If a monster uses a polymorph trap, the normal sounds will be heard for a shapeshift. Note that if you have telepathy and you see a monster standing still and polymorphing, it could be on a polymorph trap but more likely it is a shapeshifter.
Monsters may deliberately jump onto polymorph traps if their difficulty is at most five, or simply blunder onto them. Even if monsters deliberately jump onto the trap, they still have a greater chance of becoming out-of-depth monsters than if they had used an item of polymorph.
For this reason, it's safest not to traverse the lower areas of the Gnomish Mines until one has magic resistance and is sufficiently powerful to deal with monsters like jabberwocks, liches, and vampires that can potentially be created by these traps.
If you have valuable armor which you would rather not have destroyed by the trap, you can proceed in relative safety by searching (s) every square until you find it. This strategy works best if you have high Luck. Contrary to popular belief, a pair of lenses and the enchantment on Excalibur have no effect on the chance of finding a trap. Characters with low Luck may have to search many times to reveal an adjacent trap – see luckstone, sacrifice, altar, and unicorn on how to improve your Luck. A crystal ball or confused scroll of gold detection will reliably reveal the location of polymorph traps on the level, although a crystal ball is not safe to use with low intelligence. A wand of secret door detection may be zapped in rooms to determine if a polymorph trap is present; the spell of detect unseen has the same effect.
If you do not have magic resistance, there are other ways to reliably protect yourself from polymorph traps. Wearing a ring of polymorph control is good protection against polymorph traps, as you can always choose a safe form into which to polymorph. An amulet of unchanging will also protect you from transforming. Wearing disposable junk armor while searching the level is a less desirable alternative if you must explore below dungeon level 7 without magic resistance.
The presence of out-of-depth monsters, or unusual, Gehennom-only, or non-randomly generated monsters such as woodchucks, is a likely indicator of a polymorph trap on the level. If several unusual monsters are grouped in a single area a polymorph trap is almost certainly nearby; check this with telepathy. Proceed with caution. If you are in the Mines, and either gnomes are dwarves are peaceful to you, then a grouping of peaceful monsters that should normally be hostile, no matter the depth, is a solid sign of a polymorph trap (i.e. a peaceful long worm and minotaur at Mine's End.
If you are immune to being polymorphed, you can displace your pet onto the trap to have it turn into a random monster. You can keep doing this until your pet is something useful or powerful, or turns into a (baby) gray dragon, at which point it too is magic resistant, and is no longer affected by the trap. If you aren't immune to being polymorphed, consider using a leash on your pet and standing next to a polymorph trap. Chances for a pet to walk over the trap are much higher this way. Another way is to push boulders to make a two square trap and thus forcing your pet to move between the trap and an empty space. After a desirable morph is reached, you can block the trap with a boulder.
You can also use a magic whistle to make your pet land on the trap until you get a desirable morph or a gray dragon. Combine the polymorph trap and magic whistle with some pet treats like tripe or a horse friendly treat like an apple and you can get a pretty nice pet. Note: pets that eat in your presence tend to stay tame longer. The winged gargoyle is a great pet, but it doesn't eat. Standing on the trap and displacing the correct pet onto it works best. Each move, you have 6/7 chance of swapping places (never if it's a long worm or you are punished), 1/7 chance if it is sessile.
If you have neither magic resistance nor a magic whistle, you have no way to cause a sessile pet to be polymorphed by the trap; generating one of these (such as a blue jelly), would end the attempt, but at least protect the trap from other monsters.
If your pet is polymorphed into a pudding, you may want to try to split it, possibly yielding more pets to polymorph. As the name is cloned along with it, you may want to rename one. See Abuse for ramifications of attacking and splitting your pet. Follow the usual advice on splitting puddings if you are not familiar; doing this carelessly is an easy way to accidentally kill your pet.
Polymorph traps are a resource, but they can also be quite dangerous if you leave them lying around unprotected (some weak but intelligent monsters will willingly jump into the trap to become something stronger (luckily including pets), which can be a Bad Thing depending on how much stronger it becomes). In NetHack 3.4.3, you could protect a polymorph trap by dropping an item and engraving Elbereth on it. This would prevent most monsters from stepping onto the trap. Alternatively, if you didn't have protection from the trap, you could drop an item and engrave Elbereth on each tile adjacent to the trap. You can also dig down on the polymorph trap with a pick-axe: since only one trap can exist on a square, the resultant pit will remove the polymorph trap. Pushing a boulder on the trap will only protect it from most monsters – notably, very small ones can still use it. (In case no boulders are handy, you can make a boulder fall down stairs by throwing a non-rock object onto it.)
- mklev.c in NetHack 3.4.3, line 1231
- polyself.c in NetHack 3.4.3, line 266: dragon armor polymorph
- polyself.c in NetHack 3.4.3, line 277: lycanthrope polymorph
- polyself.c in NetHack 3.4.3, line 282: vampire bat polymorph
- polyself.c in NetHack 3.4.3, line 396
- polyself.c in NetHack 3.4.3, line 452: time-out for polymorph
- trap.c in NetHack 3.4.3, line 2121
- mon.c in NetHack 3.4.3, line 2412
- mon.c in NetHack 3.4.3, line 2376
- trap.c in NetHack 3.4.3, line 1253: monsters may resist polymorph traps
- find_misc in muse.c
- use_misc in muse.c
- monmove.c in NetHack 3.4.3, line 1049
- muse.c in NetHack 3.4.3, line 1789
- uhitm.c in NetHack 3.4.3, line 318
- uhitm.c in NetHack 3.4.3, line 338