There should be a Dexterity saving throw against taking fall damage when you fall through a hole or trap door and land on a different floor.

Boots that act like the Hover Boots in The Legend of Zelda: Ocarina of Time. They do not actually make you levitate like boots of levitation will, but will instead delay falling for a turn or two, so you can cross holes, pits, and 1 or 2-square wide liquids like water. If you stay still on the space without support and let the timer run out, you will fall. In order to mislead the player into thinking they might be water walking boots, they may give no special message when activating.

Not specified if this should be an ordinary random piece of magical armor, or a minor artifact.

Fall damage from falling through a trap door or hole should be significantly reduced if you happen to land on grass.

Holes and trapdoors should be made determinstic, by doing the following: Any time something uses a hole or trapdoor, seed a special RNG with the x, y, and z coordinates of the hole or trapdoor, and use it to generate the destination level. Store the RNG state with the migrating monster or object (or player), and use it again when that level is loaded to select a landing spot.

Various effects for armor pieces based on their randomized description:

• Buckled boots and old gloves: cost (and sell for) twice as much in a shop.
• Hiking boots: prompt before walking into known pits or holes.
• Mud boots: autocurse when worn.
• Padded gloves and visored helmet: +1 to AC.
• Tattered cape: -1 to Charisma.
• Ornamental cope: +1 to Charisma.
• Opera cloak: some sort of bonus when using musical instruments.
• Plumed helmet: +1 to Charisma, -1 to Dexterity (or have these adjustments multiplied by its enchantment).

The “Construction Patch”:

• When digging out stone (not necessarily walls) with a pick, rocks may fall on your head with a lowish chance, about 10% per dug square. These deal the least damage if you are wearing a dwarven helm, and a little less than normal if you are wearing some other hard helm. Dwarvish characters have a high chance of dodging the falling debris entirely. Possibly also allow a boulder falling on your head from digging similar to when monsters tunnel.
• You can apply rocks at an adjacent floor square to build a wall. It takes 50 rocks, or 25 if there is a boulder in that square. (If the space is marked as being wall-nondiggable, this either doesn’t work, or flips the space to being diggable.) It takes 1 turn per rock to build it. In the process it creates an immovable object or dungeon feature called “partially-built wall” on that space, which tracks how many rocks are part of it. If you move onto the space, you can dismantle the wall and retrieve the rocks.
• You can apply rocks at an adjacent pool or moat to attempt to fill it. The more rocks, the higher the chance of filling it. This takes only 1 turn.
• Stone to fleshing diggable wall turns it into huge chunks of meat.
• Force bolts from striking wands or the spell scatter rocks off diggable walls they hit, and in roughly 5 shots the wall is destroyed.
• Digging a pit or hole puts a pile of rocks on a random adjacent square.
• When you dig a hole and fall down to the next level, you are usually accompanied by a shower of rocks falling on and around you. Dwarves are more adept at dodging and getting hit by fewer rocks.
• When using a pick to dig a square of natural stone where the four orthogonally adjacent squares are all dug out already, you are asked if you want to carve out a boulder. If you say yes, a boulder is deposited on the new space.

Note that the two boulder-creation methods above run the risk of being exploited for abusable quantities of food if you have stone to flesh available, and the stone-to-flesh-walls method explicitly invokes this.

When digging a pit, there is a (10 - (Luck/2))% chance that you break through to the floor below, creating a hole instead and falling through.

Occasionally, if a Mines filler level generates where there is a sufficiently large space of empty stone, a little separate walled-off area may generate disconnected from the main map, containing a few gnomes and dwarves, and some more gems and gold, possibly in a chest. This area won’t get the stairs generated in it, and should probably contain a hole so that a randomly teleporting player won’t get stuck there (other types of escape items could get picked up by the gnomes and dwarves).

A statue that falls into a pit or hole fills it up like a boulder would.

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 flavored as the monster lurking by the shaft in order to catch easy prey.

Remove the air currents in Sokoban that prevent you from floating or flying over the pit and hole traps. Instead, apply the normal luck penalty. Though it’s been pointed out that this would allow a player to bypass the entire branch and then negate the whole luck penalty if they can find or create a coaligned unicorn and throw a few gems at it.

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

Occasionally when a pit or hole is generated, generate a random cloak on top of it (it’s poorly covering the opening and the hero doesn’t notice until they either search while next to it or step onto it).

Holes always drop you exactly one level (though trapdoors may still go farther).

When you step onto a pit or hole, your chance of falling in is based on your Dexterity rather than being the usual flat 20% chance for traps.

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

More harassment effects: the chance of respawning the Wizard is a fixed 1/7 and the rest of the effects are equal probability. Multiple non-duplicate effects may happen at the same time.

• Unchanged: curse items, summon nasties, vaguely nervous, aggravate monsters
• Darken much of the level, and extinguish, destroy, or cut the remaining lifetime of light sources. Maybe also blind the player.
• Drop boulders around the upstairs, or iron bars.
• Spawn pools centered on the player, with sea monsters in them.
• Spawn lava around the level, not under the player.
• Create a hole or pit under the player.
• Create a stinking cloud centered on the player.
• If you are carrying the Amulet, it teleports to a random square on your level or the level below.
• If you are carrying the Amulet, it (and possibly any fake Amulets) becomes heavier. This either lasts until the next harassment triggers, or is permanent but the total amount of weight added to the amulet has some sort of cap on it. This is interesting primarily because it targets carry cap, which is a valuable end-game resource.
• A variety of powerful player debuffs such as dealing half damage, taking double damage, blocking HP or Pw regeneration, super hunger, etc.