Define several generic monster strategies, which a monster will follow to the best of its ability, and can be swapped out for other strategies given certain triggers:

• Default: Monster roams aimlessly unless they can see hostiles, in which case they beeline towards those hostiles. Smarter monsters might remember the last place they saw a hostile and beeline towards that square when the hostile goes out of sight.
• Lure: Active only when a monster is fleeing and knows about a trap in the vicinity. It tries to get the trap between itself and you.
• Blocking: Monster tries to get between the player and a certain space. Won’t work well when there’s only one of it, but will do nicely in small or large groups.
• Zombie resurrection: If zombies can resurrect each other through physical contact, living zombies will try to move towards zombie corpses they can see.
• Throw weapon versus wielding it: Mostly useful for things like daggers or knives. Most monsters should be smart enough not to throw away their last melee weapon when they know they can hit for more damage with it. They will, however, unwield weapons and hit you with fists if their only weapon left is grossly unfit for melee (i.e. crossbow).
• Darkness: Try not to move out of darkness / into darkness unless there’s no other choice. If in the wrong one and doing nothing special, beeline towards the nearest visible way out of it. Most useful for gremlins who want to stay in darkness.
• Passwall: if monsters cannot take physical items with them when they phase through walls, they will not actually pass through walls while carrying any items they care about, unless they are fleeing, in which case they will abandon the items.
• Food smells: If the hero is carrying a lot of food in open inventory, monster AI may be more effective at tracking the player, depending on if the food is anything the monsters like to eat. Carrying around lots of fleshy food like tripe rations or meatballs helps carnivorous monsters track, carrying around produce helps herbivorous monsters track, tins don’t have any scent or effect, inediate pets get no tracking bonus.
• Hero displacement: Monsters often attack each other because they think the hero is displaced where another monster is. The smarter a monster is, the more chances it should have to re-roll this displacement roll as long as it keeps landing on other monsters. Or else, if there’s only one displaced image, smart monsters should conclude it’s not where the other monster is and lash out randomly at empty space.
• Bones ghost AI: camp on the bones pile, guarding it, never chase the hero away from it.
• Insects returning to the hive: bees periodically path back to their hive unless they’re actively chasing or combatting something. Ants do this too, and even pick up and bring back food items.
• Swarming AI (bees and possibly other insects): before moving, they calculate if they can see any others of the same monster, and if so, they are disincentivized for moving into a space where they would lose sight of all such monsters. This should keep swarms actually cohesive but still able to move along corridors and pursue the player.
• No reason to move: the monster doesn’t move, or moves infrequently and randomly, unless it sees you as an enemy. It can have a normal speed and doesn’t need to be sleeping or peaceful or anything. If it no longer detects you, it may return to its state of not pursuing you.

You can enter into a pact with a single non-unique demon of your choice over the course of a game. This gives you significant benefits (varying and according to the type of demon) but also major disadvantages for the rest of the game. One major disadvantage for all demons is that it becomes much harder to be in good standing with your god.

Other examples of advantage/disadvantage pairings:

• A +8 damage bonus in exchange for being unable to become fast or very fast
• Being able to cast any non-healing spell in the game in exchange for no natural heath regeneration
• Maxing out an attribute in exchange for permanent reductions in your other attributes

Deafness multiplies your spell failure rate by a constant amount, due to maybe not getting the pronunciation right because you can’t hear yourself.

The potion of levitation has negative weight, and lightens your inventory load rather than weighing it down more.

Your base hunger rate is adjusted slightly up or down based on the amount of weight you’re carrying.

Whenever you arrive on a level through a portal, either the portal moves a short distance or you appear a few spaces away from it. Or turn all 2-way portals into paired 1-way portals which can have different arrival coordinates defined.

Turn kicking a door into an occupation: you’ll keep kicking it until you get interrupted somehow, or successfully kick it down.

Boots with the random appearance of “hiking” slightly decrease the speed penalties if you are encumbered.

Scroll of religious text, which can be read for a prayer (or opportunity to pray) that ignores your prayer timeout.

Explosions destroy diggable walls.

Rope golems sometimes drop leashes, bullwhips, or grappling hooks upon death.

Artifact wand of striking whose damage increases with its recharge count. Its odds of exploding on a recharge are lower than usual for wands.

Artifact weapon that creates a shockwave upon hitting a monster, dealing minimal damage to other monsters behind it.

Replace the mysterious force with “dark energy”, which starts pooling from the high altar of Moloch soon after you get the Amulet, and thereafter from the downstairs of a given level. If you are caught by the dark energy, you start taking a bunch of damage, limiting the amount of time you can spend on levels after getting the Amulet.

Chargeable ring that reduces incoming damage (perhaps by half, not triggering if half physical or half spell damage applies from some other source) but may lose a charge every time you take damage.

A spell that lets you mark a tile within some radius. A few turns later, any monster on that tile is dealt significant damage.

If you have very high strength, kicking open a door can cause it to be knocked off the hinges and land on top of a monster behind it.

The #attributes screen gives you several time-related pieces of info:

• The current time as observed by the game. (Possibly it should just tell you whether it’s night or midnight).
• How long it has been since you started the game in wallclock time, for speedrun checking.
• How long your current session has been.
• The current phase of the moon.

A intrinsic that negates the single next instance of HP loss, and then goes away. Possibly granted by a spell.

Let the player type “bgf” at a wish prompt and alias it to “blessed greased fixed”.

Thick woolen socks, worn in the boot slot. Give no AC, but provide cold resistance.

Engraving (or ward) that is bad/cursed, and it causes bad things to happen on or around it. Anti-Elbereth of sorts. Monsters may deliberately engrave it to hurt the player.

Ravens flee from straw golems, who are basically scarecrows.

Object property “frost walker”, which only generates on boots. When worn, lava cools into solid floor and water freezes into ice in a radius 1 around the wearer. Optional if they unfreeze afterwards. Alternatively, make this an artifact pair of water walking boots.

Give a different message for when you injure your legs by kicking. Possibly as subtle as “Ouch! That really hurts!”, but could be more explicit like “Ouch! You injured your leg!”

Wearing armor made of gold increases your Charisma by 1 or 2 for each piece worn (possibly even bypassing racial maximums).

When you are polymorphed into a sea monster, you can sit on fountains and drink potions of water to regenerate HP.

Alarm trap on doors: it makes a noise to alert nearby monsters, and also summons a squad of ogres or Kops or whatever on one of the stairs.

You can pray at a gravestone, or possibly ring a bell at one, to cause any of a number of good and bad effects:

• Summon a ghost, which might be hostile or peaceful.
• Summon a hostile undead, flavored as it forcing its way up out of the grave. Usually a zombie.
• Polymorph you into a zombie or mummy of your own race.
• Put you to sleep, ignoring resistance.
• Create a swarm of hostile manes or lemures.
• The headstone falls on your foot, dealing some damage, less if wearing boots (“killed by a falling tombstone” if fatal).
• If the grave is a bones pile grave, the ghost of the player always appears. It will be peaceful if their alignment matched your own and hostile otherwise.
• Various cosmetic messages that do nothing. “The air suddenly turns cold.” “The engraving on the headstone shimmers for a moment.” “A shiver runs down your spine.”
• The dirt cracks open and spits out any items buried under it.
• A voice from nowhere whispers a random rumor, true or false.
• The epitaph on the grave changes. This does not flag the grave.
• Get an alignment bonus for honoring the dead (this is only if triggered by praying). “You feel that the one buried here is content.” Bonus might be larger if you’re lawful or a Priest, probably 1 otherwise. This should possibly happen before and independently of any other effects.
• Limited identify of 1 item.
• Type-identify of multiple un-type-identified items in the inventory, but the player doesn’t get to pick which. Might pick 0 items (flavored as the spirit not knowing anything new about what the hero is carrying).
• Enlightenment.
• Temporary telepathy / sleep resistance / infravision / other intrinsic.
• The gravestone rumbles and moves aside, revealing a branch staircase to a just-created-now one-level branch, a small one-off “crypt” floating branch that contains some undead, some boxes containing corpses, and some treasure.
• You “feel that the dead are restless”, aggravating monsters level-wide. All gravestones on the level become flagged against further attempts. This effect could be added to and independent of other ones, and if so, it’s a chance dependent on the number of already flagged gravestones on the level, which provides a nice way to balance it on levels that have massive amounts of gravestones.

After you get one effect, the gravestone is flagged so that it doesn’t happen again (or, more evilly, that any further attempts will only result in bad effects). Possibly shouldn’t work at all on graveyard levels, because they have too many graves to balance these effects.

Slime terrain or puddles of slime, left behind when P-class monsters move around. It either deals damage or erodes footwear to stand in it.

Dipping or dropping gold pieces in a fountain very rarely increases your Luck.

Chatting to monsters gives different various effects depending on your current form and the other monster. For instance, chatting to an orc as an elf or vice versa will make them hostile.

When Fire and Frost Brand come into contact with water due to rust traps or dipping them in fountains, print a message about the water instantly evaporating or freezing. If either is dipped into a fountain, it dries it up.

Some means of leaving an engraving on the ground for the next player who reaches that floor to encounter (not a bones file, just a random engraving).

Item called “message in a bottle” that sometimes generates near water sources. You can read it to get a random rumor.

Drinking booze while already under its effects, or occasionally when its confusion effect wears off, causes hallucination.

New monster “master grid bug”. When they zap you, you get a status effect that forces you to move only orthogonally like a grid bug for some time.

Allow scrolls to generate as metal, flavoring metal scrolls as engraved plates. These cannot have their labels wiped and cannot have new labels written on them, but they are immune to fire and water damage.

Enlightenment tells you how many more turns you have for timing-out effects.

When fountains dry out, they become empty fountains instead of disappearing (possibly turning its { to white or gray?). There is something you can do to restore the water to a dry fountain.

Dirt terrain, behaves the same way as stone but digs faster.

Potion that keeps your HP from dropping below 1 for a limited time.

Sensitive eyes intrinsic: you can see farther in the dark, but anything that creates light such as the scroll or a camera will blind you.

Deployable barricade on a tile. Blocks movement; must be attacked or kicked several times to be destroyed. Presumably lightweight to actually carry around.

A wand that, when it hits a creature, saves that creature’s position and forces it to teleport back to that position after a few turns.

Scroll that restores you to full health but decreases your maximum health.

Ring or amulet that causes your spellcasting to draw on HP instead of Pw, possibly only when your Pw is zero, or possibly not requiring a ring. Each point of HP is worth 2 Pw points. If cursed, doubles spell Pw costs. If blessed, energy regeneration will regenerate HP until full before regenerating Pw. Casting from HP too much may decrease your HP maximum. If implemented as an artifact, possibly flavor it as an evil counterpart of the Eye of the Aethiopica.

Note that a couple variants have implemented this as a “ring of blood magic” or similar items.

Dungeon branch or level filled with toxic contact gas (breathless doesn’t help, or only helps a little) so that you constantly take damage and must bring a lot of healing with you. The deeper you go, the worse the gas becomes, but the loot gets better.

Scroll that tells you the dungeon overview for the next 5 levels of the dungeon. If blessed, shows more levels; if cursed, shows fewer levels or omits details.

Lure, which attracts monsters to you. Could be a magical non-consumable item, or a charged item that amounts to spraying yourself with scents. The Amulet of Yendor should also have this effect, at its maximum level at all times.

Spell that grants temporary hit points.

Temporary hit points and Pw: your maximum goes above its normal bounds for some time, before returning to normal. If your normal maximum changes for some reason, the temporary maximum changes by the same amount. There are two proposals for how the effect should end:

• The entire effect is timed, and once it ends the temporary buffer vanishes. If your HP would go below 1 as a result of this, you could either die or have it set to 1, depending on implementation.
• The temporary buffer drains away at the rate of 1 point per turn, and the effect naturally ends once it’s gone.

Split curse resistance off from magic resistance. Curse resistance is granted only as an extrinsic by a couple of artifacts, including Magicbane, and ‘‘maybe’’ some mundane item that isn’t any good otherwise (a mummy wrapping?), and behaves like Magicbane’s curse resistance does currently (“You feel a black aura surround the [item].”) Half spell damage without curse resistance no longer helps limit the number of cursed items, and a curse may still manage to bypass resistance, with current probabilities. There could also be an amulet versus curses.