When you vomit, you are prompted to choose a direction in which to vomit. The space in that direction is then hit with a weak acid attack.

Deeper in the dungeon, rust traps might target your pack instead of your armor or gear, and could possibly be renamed to “water trap”. On deeper levels and particularly in Gehennom, rust traps phase out to be replaced by acid traps. These deal corrosion and acid damage (and quite a bit of it, like having multiple potions of acid dumped on your head).

Getting hit with acid can decrease Charisma.

If you are turning to stone and take acid damage from any source, the stoning is stopped.

Generalize cockatrice-egg mechanics to all eggs: eggs of acidic monsters will be acidic, eggs of poisonous monsters will be poisonous. Possibly even have a (reduced) chance of getting intrinsics from a monster egg.

Pool of acid terrain that deals severe damage and corrosion if you fall in.

You can dip an item in a ochre, spotted jelly, or acid blob corpse to make it take acid damage (if applicable).

A troll killed by fiery or acidic means (including Fire Brand) cannot revive.