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.

Occasionally, maybe 1% of the time a monster spawns during normal gameplay (not during level creation), select a random stair on the map as its spawning location, even if the player can see those stairs. This makes it appear like the monster is arriving from off-level.

However, first scan the stairs and the 8 spaces surrounding it to see if any monsters or the player are there. If so, do not do this and instead spawn the monster randomly like normal.

Allow downstairs to be marked as “secret” so that they don’t show up unless searched for or by stumbling onto them (in which case you fall down them). Use this specifically for early hidden branches, like Goblin Town in EvilHack.

When you pass out from eating rotten food while standing on a staircase, you fall down the stairs (likely petrifying you if you are carrying a cockatrice corpse) and “find yourself at the bottom of the stairs” when you come to.

Stairs should show any annotation of the level they lead to. Probably not by default, instead when using the nearlook and/or farlook command.

E.g. “There is a staircase down to level 2 (MUMAK BY THE STAIRS!!) here.”

Revamp Gehennom by making its main branch substantially shorter, a “hub” branch containing stairs or portals to a bunch of sub-branches containing demon lords’ lairs. Most of the lairs are optional, but at least some of them are required in order to enter the Sanctum. Each demon lord that you don’t kill, however, incurs a unique, harsh effect or debuff on you once you have the Amulet. Suggested ones include:

• The mysterious force, as it exists in vanilla.
• When you try to ascend the stairs, they vanish and several illusory copies of stairs appear across the level, along with one real one which you have to find.
• Walls extrude from existing walls around the hero in random directions, never entirely closing off, via a cellular automaton that looks for walls with a 3x2 area of walkable spaces in front of them, with the space directly in front a regular floor space - the effect of this given enough iterations turns the terrain around you into a maze.
• Generic damage over time, not severe but enough to provide a headwind. Or partial or total disabling of natural regeneration.
• Asmodeus: Some damaging cold effect that happens periodically, or your cold resistance is nullified and replaced with a vulnerability to cold effects.
• Baalzebub: Something to do with insects, either periodic summon insects from nowhere or stronger/more frequent insects
• Juiblex: You may randomly become ill, or have your regeneration dampened or something
• Geryon: Hordes of buffed q generate and rampage periodically.

You can throw an item down stairs by standing on them and throwing the item >. This makes the item go through the normal fall-down-stairs routine.

The higher your encumbrance level is, the more damage you take by falling down the stairs.

If you are on a staircase/ladder (maybe a magic portal), your pets will always try to approach you (using the appr = 1 code path in dog_goal). Maybe, to make it a little less obvious have pets approach you (with a less than 100% chance) if you are merely near the stairs, with a diminishing chance of intervening to set appr = 1 the farther away you are.

Throwing something downwards on a down staircase will throw it down the stairs, making it end up on the level below.

Walking up stairs exercises Strength.

If you try to go up or down stairs or enter a magic portal, and there is a pet that is still eating next to you, you are prompted to confirm changing levels. Also remove the “foo is still eating” message since it will then be covered in the prompt.

Upper Mines levels’ stairs are biased to generate relatively close to each other.

Level 1 divination spell “waypoint”, which reveals the location of all stairs/ladders (but no other spaces) on the level. Does not work if the level is unmappable.

Monsters may spawn on the upstairs or downstairs in sight of the player; this is easily flavored as them coming in from other floors. If the monster selected spawns in groups, it picks somewhere that isn’t the stairs, though.

When you use stairs, not only do adjacent pets follow you, but any pets adjacent to adjacent pets, and so on, also follow you.

When trying to descend stairs while stunned, and possibly confused with some probability, you fall down the stairs.