New “true vegan” conduct, which is broken by using any animal product whatsoever, such as leather-based armor, anything made of bone including unicorn horns, anything made of dragonhide, tallow candles, etc. Picking up the items is okay but applying or equipping them is not.

Outside the Plane of Air (where there is no gravity), stepping onto air terrain automatically makes you fall to your death unless you are levitating or flying. (Or possibly you merely fall to a lower level, taking a fair amount of damage, or you have so far to fall that it takes a couple turns to hit the bottom, in which you have a couple turns to take some action to save yourself, by levitating or flying or whatever). However, you are prompted to confirm stepping out into the open air if it isn’t safe to do so.

Items dropped into open air either end up randomly placed on a lower level if there’s a sensible lower level to place them on, or vanish forever (though in that case an exception needs to be made for the unique items).

If falling into air is an instadeath, life saving acts the same as if you die in lava; it puts you on a safe location (“You find yourself back on solid land again”).

Air can use the W_NONDIGGABLE flag, or possibly one of the other struct rm flag bits, to represent a wind barrier, which the level designer can use to make a region of air impassible. Attempting to move onto such a space produces a message like “A strong gust blows you back!” and makes you lose the turn.

One of the greatest problems with air terrain is what ASCII character to display it as; existing implementations use just regular space (which is what it displays as on the Plane of Air), but this is easily mistaken for stone, which can lead to players unexpectedly falling to their death if there is no safeguard against wandering off a cliff, and would present a problem if there were ever a air/stone boundary, which would be invisible. Other suggestions include: space, but highlighted with the terminal’s black color ( ), black pound sign (#), black tilde (~), black right brace (}), or even just gray counterparts of these. All of these have various downsides; for instance, it must be expected that they will render as dark blue for some players who have use_darkgray turned off.

The Candelabrum refuses to light if it has fewer than 7 candles.

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.

The scroll of scare monster, on the ground, will do a check versus monster magic resistance before it actually scares a monster.

q class monsters should have their difficulty rebalanced to at least roughly reflect their damage output; mumakil are the strongest q of all and have one of the lowest difficulties.

Sunglasses, an eye-slot tool that protects versus being blinded by flashes of light from things like lightning bolts, cameras, and yellow lights, either completely or with an 80% chance. (They probably shouldn’t block blinding from spat venom.) May also block certain gaze attacks. They should have some downside when worn, such as limiting your maximum vision radius or impeding searching.

Tourists start with a pair of sunglasses.

Certain monsters (intelligent ones like Elvenkings that are smart enough to realize you probably will kill them) turn peaceful or generate peaceful depending on your XL.

Add a scroll of polymorph. Blessed polymorphs you with polymorph control over this one occasion; uncursed polymorphs normally; cursed polymorphs you and everything adjacent to you.

The scroll of remove curse’s blessed effect is transferred to its uncursed effect. The blessed effect is now to uncurse everything in inventory, and then bless a few items. The cursed effect now randomly curses inventory as the curse items spell would do. May need to make this scroll rarer or more expensive to write in order to keep it balanced.

Jetpacks, a chargeable source of levitation/flying. They are worn in the cloak (or body armor?) slot and grant 0 AC.

Ovens, a dungeon feature (\) that you can use to cook food, light items on fire, and test potions in a safe, controlled manner like you can with rings and sinks. This happens by putting the potion in the oven and it produces some cosmetic message that can be used to identify it.