New “flooded stairs” terrain type. They act normally as stairs, but are also treated as three-dimensional water (that you cannot fly over and must be submerged in, like on the Plane of Water). This would not be very useful on its own but would be a building block for quests or other special levels that are entirely underwater.

Getting hit in the head by a gush of water from a rust trap, or being immersed in water, immediately removes any cream pie on your face.

Inventory wetting triggers every turn you are submerged.

Water turbulence won’t affect your underwater movements unless you are trying to move from one water square to another water square, and the water square you are on has at least one orthogonally adjacent water square.

If you have swimming, you can use , to pick items up from underwater.

If you try to drink a potion underwater, it will first go through the normal dilution routine. This means that an undiluted potion will become diluted (but will generally be fine to drink), a diluted potion will become water (and thus useless), and a potion of acid will blow up in your face.

Dungeon branches that are completely submerged: their levels have a special level flag that treats you as underwater no matter what the terrain is. Would work better if a breath timer were implemented rather than instant drowning if a magical breathing source is lost. Trying to go down the stairs leading into the branch without the ability to survive underwater is equivalent to jumping into a pool: you will get wet and then crawl out (still on the stairs), without changing levels.