A ring of monster attraction: Each individual ring is associated with a randomly selected specific, common monster species (or possibly monster class), and causes monsters of that species/class to generate disproportionately often while it’s worn. When the type is known, the ring appears as “ring of monster attraction”, but when an individual one is fully identified, it ring appears as e.g. a “ring of newt attraction”.

Depending on the potential for abuse, it should probably not be allowed to wish for specific monsters. E.g. it’s probably bad to allow the player to wish for a ring of wraith attraction.

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.

Mithril dragon, a dragon which spawns only if you (or possibly any creature on the level) is carrying over 75 aum of mithril in open inventory. It eats mithril items (and only mithril items, rather than being generally metallivorous).

Ravens are always generated peaceful for Valkyries (or maybe only neutral Valkyries, since they follow Odin).

In order to add variability between different games, at the start of every game, “theme” objects and monsters are selected, which are outsizedly likely to generate. For instance, one potion type becomes the “theme potion” of the game, and then 10% of all randomly generated potions are that potion, and a wand type becomes the “theme wand” and 10% of random wands will be that wand.

Three theme monsters are picked, one low level, one medium level, and one high level. The probability for them generating when a random monster generates should probably be lower than 10%.

Create a new stat to track the maximum level a player has ever reached, named “u.ulevelpeak”, and use it when computing the difficulty monsters should generate at, so that the player has no incentive to drain levels from themself to get easier monsters.

ulevelpeak is used rather than the existing ulevelmax because ulevelmax represents the highest level it is possible for the player to return to via restore ability, and shrinks when doing things such as quaffing blessed full healing to restore lost levels and losing levels when polymorphing into one’s own race, so it’s unsuitable for the monster generation purpose.

After killing certain type(s) of monsters (such as the monarch of a throne room), a timer may start that spawns an avenging posse of related monsters nearby.

In addition to making Gehennom much more open, make the monster generation rate much higher, so that players are encouraged to traverse them quickly and avoid being overwhelmed rather than spending lots of time searching every cranny and becoming bored.

If adding a new centaur designed to be a significant threat increase over the existing ones, they should generate with good (if non-magical) armor and a good weapon, which is frequently a lance. If they have a lance, they will use it to joust you.

Croesus may generate disguised as another @, possibly hidden among his soldiers.

Every 5000 turns, the monster generation difficulty increases by 1. Effectively changing the formula to be (your XL + dungeon level) / 2 + (turns / 5000).

Unicorns are more likely to generate peaceful if you are celibate and have not yet dallied with a foocubus in your game. (Since coaligned unicorns are peaceful anyway, this would affect cross-aligned ones only.)

Monsters that generate in branches associated strongly with an element (e.g. Gehennom, and the Ice Queen’s Realm) should automatically be given resistance to that element, even if they wouldn’t get it normally.

Track the amount of time the player has spent on a given dungeon level. As it increases, random monster spawns gradually get less frequent (unless you have the demigod flag set, which overrules this) and more difficult, starting at one or two thousand turns spent on the level.

In special rooms with zoo-like generation, meaning they generate a monster on every square, generate the monsters with MM_NOGRP to suppress group generation. This prevents a group from being one of the last things to spawn into the room and overflow into nearby spaces outside of it.

New special room “cursed graveyard”. Its initial generation is the same as a regular graveyard. The difference is that it generates undead monsters on open spaces in the graveyard (with messages like “A zombie claws out of the ground!”) at a much higher frequency than normal, so long as there is still a gravestone existing within the graveyard. When all gravestones in the graveyard are destroyed, the room converts to a normal graveyard and undead stop spawning.

Gravestone texts in a cursed graveyard don’t draw from the regular pool of gallows-humor messages. They instead use a separate pool of ominous, vengeful, and threatening messages.

Regular gravestone-destroying penalties do not apply if the gravestone being destroyed is in a cursed graveyard.

Priests can destroy a headstone in a cursed graveyard by #turning while standing on it.

Monster generation in the Mines automatically selects a G monster on 1/6 or 1/8 of all spawns. It’s odd that the branch’s lawful bias means that dwarves tend to appear over time, but not gnomes.

Baby owlbears, unlike regular ones, aren’t specified as M3_HOSTILE, allowing them to occasionally generate peaceful for neutral characters.

Allow quest monster generation to be specified more precisely than having a fixed set of probabilities for two specific monsters and two monster classes (e.g. the Wizard quest has a certain distribution of vampire bats, B, xorns, W, and random monsters; it is not possible to change this distribution without changing it for every quest).

Implementation details: keep the definitions within struct Role, but do it with, say, a struct of { int, bool, int } repeated however many times a quest needs. The first int is the % chance out of a hundred for this struct to be selected. The third is either a PM_* monster index or S_* monster class constant. The second just informs it which of those options it is.

When generating a quest monster, the game can then roll a d100 and iterate through this array of possible monsters, decrementing as it goes, until it hits the right element; if it goes all the way to the end without hitting any monster or class it generates a normal random monster. (This is more or less the same as the algorithm for picking items generated in shops.)

The Seven Deadly Sins can generate randomly in Gehennom. They are the only uniques that do this. There is no guarantee that you will encounter all of them, or even any of them.

Possibly make it so that you need to have committed the associated sin in order for them to spawn; if you have avoided being Satiated, Gluttony will never spawn, if you are celibate, Lust will never spawn, and so on.

Rather than slowly increasing the natural monster generation rate over time, gradually increase other monster stats that are less obvious, such as HP maximum, computed level, or attack power. Though this approach has been criticized for hiding the increase in difficulty from the player, whereas generating more monsters is obvious.

Sharply cut the frequency of lizards spawning (possibly even lower than 1/7), and possibly remove the special case that makes them always leave a corpse. This is because a player will usually accumulate enough of their corpses to be easily safe from any delayed stoning effect for the whole game. This won’t much affect reverse genociding them, if the player really wants a lizard corpse.

Also, possibly elevate their monster difficulty to something higher than 6; not because they are that difficult, but to make them appear only later on in the dungeon.

Alternatively, simply make lizard corpses rot, so that a player who wants to carry around a stoning defense must use other items, such as tins of lizard or acidic monsters, or potions of acid.

Extension of the feature in several variants where monster spawns are concentrated on the upstairs during the ascension run: occasionally, instead of spawning a monster, generate an organized group which is trying to get the Amulet, usually made up of sapient monsters (such as a group of soldiers, or a few priests of the same god, or some elves led by a couple elf-lords). Possibly, this only happens after you get back out of Gehennom and are again visible to the other gods.

Track how many turns the hero has spent on a level. As they spend more time there, the monster spawn rate diminishes, provided they aren’t in the end game with its special spawning rules.

The natural spawn rate of monsters on Astral (and perhaps the other Planes) is zero.

The more gold you pay to a priest, the stronger his god becomes. Newly generated priests of that god could get better equipment, or altars of that god might be harder to convert. In Moloch’s case, Gehennom gets slightly harder if you pour a lot of gold into his temple. This applies with money donated to your own god as well, but the effects are naturally less visible since you won’t go around fighting your own priests or converting your own altars.

Add a level attribute which serves as a multiplier for the monster spawn rate on that level. Can be specified in des files.

Confused genocide (uncursed or blessed) does not genocide you. Instead, it sets a level flag that prevents any more monsters from spawning on that level via the normal mechanism for the remainder of the game. (Monsters already created are unaffected.)

When you trigger the Kops, it doesn’t immediately summon massive swarms of them all at once. Instead, it triggers an effect that lasts 50+d50 turns, which causes one Kop to spawn on the upstairs and downstairs each turn, and occasionally on random spaces. Reconciling with the angry shopkeeper cancels the remaining duration of the effect and vanishes any existing Kops on the level.

This might have odd interactions if you leave the level while Kops are still spawning. Perhaps it should internally be tied to the level structure, not the player or a global variable; the effect would be suspended while off the level and resume once you reentered it.

Monsters that generate with weapons should automatically be wielding those weapons, unless they generate asleep or peaceful. The player shouldn’t get a free turn while they use theirs to wield the weapon (notable with player monsters on Astral).

Croesus is generated with 2 random amulets and 5 random rings (bling) in inventory.

Skeletons can spawn in places that aren’t Orcus-town.

The monster generation rate in the Quest gets reduced to almost nothing once the nemesis is defeated.

Alternatively, monster spawn rate in the quest is very, very low, and more monsters are generated with the level.

Alteratively alternatively, defeating the nemesis removes the Quest-specific monster generation; newly generated monsters will be random like ones outside of the Quest.

Any G that generate inside the wine cellar secret area in the Gnome King’s Wine Cellar are automatically hostile regardless of the player’s race or alignment.

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.

Monster generation in the Quest, when calculating your experience level, takes the maximum of your actual level and the minimum level required to receive the Quest.

Randomized clan names for samurai player monsters (or a single randomized clan name applied to all enemy samurai in the Quest).

When a packrat generates normally, a random item is created that it carries.

Special candle found generated in Gehennom. While one is lit on a level, it suppresses spawn rates and makes the difficulty about what it is now (without the candle lit monsters will generate at a much higher difficulty). They should be fairly nonrenewable, perhaps wishable but not polymorphable. This limits your duration of time in “easy Gehennom” before it gets harder. The candles work the same outside Gehennom, but are less useful (maybe they specifically suppress demon spawns).

The player’s own ghosts generate peaceful (possibly only in bones files).

The maximum difficulty a monster can be generated at is independent of player experience level. Only the level difficulty (and perhaps other player-independent stats such as branch) matter. The details of how the curve of monster difficulty compared to level difficulty should look are up to debate; NetHack4’s is a piecewise function that climbs slowly until level 10 and thereafter is (level difficulty - 5).

As a more minor version of this, only enforce this rule during level creation, and respect experience level for monsters generated after creation.

One or two softball easy player monsters that generate early in the dungeon, with mostly starting gear, and are not hard to kill.

Leprechauns are occasionally generated with a sack of gold rather than gold pieces in free inventory. Though this would either have to be quite rare or only be possible on leprechauns generated outside leprechaun halls.

The monster spawn rate gradually decreases the longer you spend on a level. (May not apply if you have the demigod flag set or are carrying the Amulet.)

Scale monsters’ hit dice bonuses based on their size. In order to reduce the high amount of variance monster HP currently has, monster HP is now computed by this formula: (HD)d4 + HD\*2\*(size), where size is 0 for MZ_TINY, 1 for MZ_SMALL, and so on.

Mummies have a curse item attack that would probably make them not fun to have in their current quantities. So mummies are not randomly generated; they appear in graveyards and some special levels like the Catacombs and the Archeologist quest, but otherwise do not appear.

When a monster decides whether you are peaceful and makes race or alignment checks to do so, they do it based on polyform, current alignment, and when they first spot you as opposed to when they are first created. If the player polymorphs into an orc and some other orcs are hanging out in an unexplored room across the level, they should be peaceful to the character as long as the character is polymorphed into an orc (but will turn hostile when she changes back).

Add some region code preventing monsters from generating in (or even better, moving into) the pit corridors in Sokoban until the level is solved.

King monsters should spawn with an entourage of monsters; e.g. a gnome king should create several other gnomes around him upon generation, with preference given to gnome lords and possibly gnomish wizards. If monster pets are implemented, they should behave as the king’s pets, and the king may generate with a magic whistle.