When you are in a polyform with a hug attack and attack a monster with it, there is a chance the monster appreciates the hug and becomes peaceful.

If you eat a lizard’s brain while turning to stone, it cures your stoning.

If you kick a boulder as a giant-race hero (or while polymorphed into one), it starts rolling across the ground as if it came from a rolling boulder trap.

When polymorphed into a mind flayer (or playing an illithid in variants that have it as a race), you gain additional nutrition when you eat the brain of a spellcasting or telepathic monster.

Vampires shouldn’t be able to harm any monsters with a bite attack if the victim is bloodless, not dealing any damage or level drain. (Also includes the player if polymorphed into a bloodless form.)

When polymorphed into a monster that has hooves, your kicks deal some extra damage, whether via the kick action or via the polyform’s kick attacks.

When polymorphed into a form that has automatic bite or other melee-touching attack, if you are about to attack a cockatrice, make it subject to an Intelligence saving throw; if you pass this you avoid attacking the monster with your body.

If you are a werecreature in your were form, you can chat to monsters of the same form to tame them.

If you are polymorphed into a nymph and are lawful, you suffer an alignment penalty for stealing items from other monsters.

Eating the brains of a spellcasting monster should restore some magic energy, and perhaps even have a chance of learning a spell from its brain. (This latter part would work better in variants such as FIQHack where monsters have a list of player spells).

Using #monster when polymorphed into a demon allows you to call for hell-p from other demons directly, without needing to hit an enemy in melee. This uses up some Pw. It may not work 100% of the time, but will cost Pw regardless of whether or not it works. Another possible restriction is that you need to be next to a known enemy for it to work.

Polymorph forms should give intrinsic magic cancellation corresponding to the monster magic resistance stat of that species: 1 MC for 25+ monster MR, 2 MC for 50+ monster MR, and 3 MC for 75+ monster MR.

If polymorphed into a voluntarily exploding monster (e.g. a sphere or light), the player can #monster to explode without actually attacking anything. (You can already do this by forcefighting thin air, so this would just add an additional way to do it and a prompt when you polyself.)

If you are polymorphed into a monster that has tentacle attacks, you can manipulate objects such as doors and containers from 2 spaces away.

Using #monster while polymorphed into a queen bee makes you secrete a lump of royal jelly. For balance, this should cost a lot more nutrition than the royal jelly contains, or have some other limiting method so you can’t use an indefinite food source to produce indefinite royal jelly.

Eating royal jelly while polymorphed into a killer bee turns you into a queen bee.

If you are polymorphed into an inediate monster, you are physically incapable of eating.

Being polymorphed into a spellcasting monster boosts your energy regeneration rate proportional to the base level of the monster you are.

If you get bisected by the Tsurugi while polymorphed into a long worm, you get cloned instead, with a tame copy of you splitting off.

If you are eating someone’s brains when polymorphed into a mind flayer, and you are very satiated to the point where you aren’t getting the full amount of nutrition from it, you do less damage with the attack because you aren’t eating as much of their brain.

Some polyform (perhaps mind flayer) that doesn’t forget spells over time while you remain polymorphed into it.

If polymorphed into a strong clawed monster like a dragon, you can make semipermanent engravings with “-“. However, if your form does not have hands, this will be slower than an athame or wand of digging can do.

When you are polymorphed into a monster with a stealing attack, you shouldn’t be able to make a normal attack and also steal something at the same time. Perhaps the stealing attack should only be made when you are barehanded, though this could interfere with martial arts.

You need to have hands in order to operate a tinning kit or tin opener.

Eating a rust monster while polymorphed into an iron golem is instantly fatal to your polyform.

When polymorphed into a paper golem, you can’t write on the floor with your finger because it would get too dirty.

Monsters apply mirrors at you if you are a nymph or umber hulk.

If polymorphed into a giant, you can pick up a door off its hinges (breaking it).

When you are polymorphed into a sea monster, you can sit on fountains and drink potions of water to regenerate HP.

If you’re polymorphed into a unicorn, you can dip your horn into potions.