A “fearless” object property for weapons or equipment which makes the wielder or wearer immune to fear effects. (This is more useful in variants which implement a fear system.)

When you convert a cross-aligned temple’s altar, there is a Cha/100 chance that you also convert the priest along with it, and they become coaligned rather than angry.

While hallucinating, the entire map (or at least the parts you can see) should be rendered in rainbow colors. If your terminal supports 256-bit color, it uses a very fine-grained rainbow rather than the simple 16 colors.

Non-coaligned priests require more money in donations than coaligned priests do to get the same benefits.

Piranhabane, an artifact rod that instakills piranhas (and possibly, turns them into tins of piranha meat in your inventory or at least out of the water).

Having a copper weapon wielded while suffering shock damage has a lightning rod effect: it causes you to take extra damage, but completely protects all your rings and wands from being destroyed.

A couple quests for roles other than the hero’s are available to complete in the game, as extra side branches. These can be accessed from magic portals in Gehennom below the Valley of the Dead.

5000 turns after you kill or get rid of the last guard in Minetown, orcs invade and transform it to Orcish Town.

A #shove command, which allows you to shove a monster back one space, and will not anger most peacefuls, for the purpose of pushing peaceful monsters out of an altar room when they start crowding the altar you are trying to sacrifice things on. (Presumably, shoving a shopkeeper or priest or anything trying to stick to a specific location would not work the same.)

There should be a way to remove confusion from pets. One simple way to accomplish this would be giving you a way to directly feed a lizard corpse to your pet, by making pets prioritize eating a lizard corpse when confused. Though this would not work for herbivorous or inediate pets.

The sleep spell has an advanced form, castable only at Expert, which creates area of effect sleep like a magic flute does.

The material of an object affects its ammo breakage chance. For instance, mithril arrows hardly ever break, whereas wood breaks a bit more often than normal iron.

Bottle of enchanted hot sauce, which you can dip corpses into. If the corpse is unsafe to eat, it will be refreshed for 10 turns.

Evil librarian monster: it is peaceful at first, but considers every spell you know to be an overdue library book, and charges you a $100 late fee per book when it encounters you. If you don’t pay, it attacks. Possibly they carry some books, and if you manage to keep it peaceful, you can loan books from it. May generate with a magic marker.

Any cursed object, not just weapons, welds to your hands if you wield it.

The Oracle blasts you with magic missiles (directionless, appearing from nowhere, so you don’t need to be in a straight line from her) if you smash any of her statues in her line of sight. She could also yell something like “That was a gift from Medusa!”

After you drink booze, you are afflicted with hiccups for some time, which on some small fraction of turns makes you throw a quivered item in a random direction or drop your weapon.

Make the potion of restore ability alchemizable somehow. Possibly with something non-straightforward but making use of junk potions, like healing + sickness.

Monks get shorter cooldowns for techniques as their experience level increases, to a minimum of 50 turns.

The arrows created by the Longbow of Diana are of your race/role’s affiliation (e.g. orcish arrows for orcs, ya for Samurai, etc), and bear the same enchantment as the bow itself.

If a player fear system is implemented: if the player is adjacent to a creature standing on a scroll of scare monster, they will become scared of that creature. Intelligent creatures will deploy a scroll of scare monster to take advantage of this.

If you get bisected by the Tsurugi while polymorphed into a long worm, you get cloned instead, with a tame copy of you splitting off.

A magical horn whose effect depends on what material it’s made out of. One effect could be pacification; another possibility is to make it a horn of summoning, with the monster type summoned controlled by the material.

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.

When you kill a demon lord, its lair becomes diggable.

Delicatessen shopkeepers chide you if you eat something while in their shop that doesn’t belong to them and that you didn’t buy from them. “Buy something or get out!”

Wearing gauntlets of power, you can snag a boulder and pull it with a grappling hook. If in Sokoban this incurs a penalty.

Closed-for-inventory shops, if you encounter them again on the ascension run, will now be open.

Caltrops: a nonmagic stackable tool that when applied creates a “caltrop trap” on your space, which damages / immobilizes / slows the first monster to enter it. Rangers and rogues excel at using them and possibly get some bonuses from them. Not difficult to untrap, though it would be nice if some caltrops could gradually be lost in the process. Maybe spreading caltrops consumes five or so of them, and you won’t always get five back during an untrap.

Polymorph potions affect all monsters adjacent to where they shatter.

Higher pickaxe skill increases digging speed.

Command (generalization of #tip, or #dump, have both been suggested) to transfer all items from one container into another container without having to temporarily place them in your inventory. It would be better but perhaps harder to implement if you could pick and choose which items were being transferred, rather than all of them.