Award some experience points when the hero discovers a trap door in a “Vlad was here” closet by searching for it (not by triggering it), because this demonstrates that they are learning that such closets contain trap doors.

When falling down a hole or trap door, monsters’ spaces are considered valid locations to land. If you land on one, you instantly kill it.

If you fall through a hole or trap door onto a level, and there is a trapper or lurker above in the area you are eligible to arrive in (because some levels constrain the region you can arrive in), you automatically land on its space and get instantly engulfed by it (with a message stating as much). This is because the monster was lurking by the shaft in order to catch easy prey.

When a trap door makes you fall multiple levels, you take fall damage (unless you’re flying).

Livelog when you fall unusually far down a shaft (4+ levels, a “very deep” fall).

Add a message for when your pet falls down a trap door and you don’t see it happen.

Lit candles get snuffed when you move next to an unseen secret door, trap door or hole: “A draft blows out your candle.”

If a leashed pet falls down a trapdoor, the player may be able to pull it back out, depending on Strength and the weight of the pet.

The number of levels a trap door will take you down is deterministic for every trap door. Possibly also extend the trapdoor and migration code to allow deterministically placing coordinates of things that fall through a trap door as well.

If hovering over a trap door and zapping an opening beam downwards, the trap door becomes a hole.