Some mechanic (maybe involving forges?) that consumes valuable gems to add enchantment to weapons or rings, because gems tend to become useless at a fairly early point in the game.

Eating a monster in front of a monster of the same race freaks them out and causes them to flee.

For every mimic you personally kill inside a shop, the shopkeeper gives you a token fee of 5 gold (or store credit) if you talk to him afterwards.

If you clear the shop of all mimics (with some minimum amount of mimics required), the shopkeeper could give you a free item of your choice.

Since crystal chests are difficult to open compared to regular containers, random ones should generate with commensurately good contents.

Artifact dart that has a 100% break rate when thrown, but if it’s carried in main inventory, it will periodically replicate itself and increase its stack size, to a maximum of 50.

Wizards receive a spellbook of magic missile as their first sacrifice gift if they don’t already have the spell in their spellbook (even if it’s completely forgotten). In this case, they get Magicbane as their second gift.

You can record the location of a stash (or really whatever point you want), and then be able to travel back to it even if you’re on another level.

When you are wearing the amulet of restful sleep, you are given sleep resistance whenever the amulet is not causing you to sleep; this is because you shouldn’t be tired in between frequent naps.

Applying a leash to a club creates an aklys.