Throwing holy water at demons should be buffed way over its current 2d6 damage, because it’s a fun interaction. Instead, it should severely weaken them, cancel them, stun them, and/or do a large amount of damage (perhaps 50% or some proportion of their max HP, possibly exempted for demon lords whose fights it would trivialize).

Add a system for casting ritual spells: more powerful and more expensive spells which have some esoteric effects you can’t get otherwise. The main differences between ritual and normal spellcasting are that they consume valuable, hopefully non-renewable components, take a number of turns to cast instead of taking effect instantly, and may require you to be in or set up certain circumstances.

Various ritual spells that have been proposed:

• Ball spells which consume a gem as focus and create a ball of elemental power that hits surrounding squares but not you. (Long casting times would probably make rituals infeasible for combat though.)
• Temporarily increase your carry cap by a great amount. (Other new intrinsics as required.)
• Resurrect a corpse as a tame monster (necromancy).
• Grant temporary intrinsic life saving.
• Single controlled polymorph with a greatly increased duration.
• Summon a demon, demon lord, or demon prince. Requires 5 cursed candles and a marker (to draw the classic pentagram). If summoning a named demon lord, it’s either random or there’s some expensive way to control who shows up. The demon lord could be peaceful, but with current behavior this is useless. Possibly summoning them allows you to make a pact with them.
• Remove the graveyard status from a level (would need to be expensive, and perhaps involve the Book of the Dead, and multiple different headstones).
• Grow a tree. This consumes at least a piece of fruit. For anti-farming the tree should probably not produce fruit or bees when kicked.
• Create a portal between two levels of your choice (doesn’t work with the Amulet obviously, but otherwise works)
• Create an artifact (that is, you somehow imbue an item with properties it can’t normally get).
• Bless items. Consumes a blessed scroll of remove curse.
• Genocide a genocidable monster. Consumes a figurine of that monster plus other costly things.
• Reverse genocide a monster. The monster may or may not have to be normally reverse-genocidable. Consumes a figurine of that monster plus other moderately expensive things.
• Charge something. Requires a rare ingredient - perhaps a dilithium crystal.
• Summon tame elemental(s). Among other things, ingredients include: a potion of water, any beatitude (water); a rock (earth); lit candles, a lit oil lamp, or a lit potion of oil (fire); an amulet of magical breathing (air).
• Create a magic lamp. Needs an oil lamp (of course) and a figurine or mask of a djinni (or possibly a nearby live djinni).
• Make the current level non-teleport. Requires a scroll of teleportation and that the caster be standing on an anti-magic field at (?) either the start or the end of the ritual.
• Create a fountain. Requires a statue of a medium-sized or larger monster, which gets destroyed (by turning it into the centerpiece of the fountain). There may be potential for wishing abuse; perhaps the fountain should be flagged so that it can’t produce a wish-granting water demon.
• Turn a regular knife into an athame. Components include other bladed weapons with positive enchantments adding up to 20 or something; all of these charges will be drained to +0 in the creation of the athame. The resulting athame is +0, regardless of the charges on the component weapons or original knife.
• Create a tame golem or golems. Requires a large amount of total weight of objects made out of the golem’s material.
• Summon a coaligned angel or other minion of your deity as a pet.
• Create a tame wood nymph from a tree (only once per tree).

Ritual spells come in spellbooks like usual, but aren’t stored in your spell list. Instead, reading the spellbook prompts you if you want to begin its ritual and tells you the necessary ingredients and circumstances you need to satisfy as preconditions. If you meet all the conditions and answer yes, you initiate the ritual. (For simplicity, this should probably burn up / expend all the components instantly.) You cannot begin a ritual while in the process of casting another ritual; this should probably be implemented as a precondition.

Apart from the component cost, rituals act as a constant drain on your Pw until the ritual is complete. If something distracts you in the middle of the ritual, you can go take care of it and then resume the ritual as long as you have the Pw left to finish it. (You could also drink gain energy during the ritual.) The only way for a ritual to fail, possibly backfiring with bad effects, is for you to run out of Pw while it is incomplete.

In addition to its preconditions, each ritual also has some postconditions: common to all rituals is that you have been casting the ritual for at least some length of time, but there may be others, such as standing on the square where you began the ritual, or have another item, or kill a monster, or something. There may also be other conditions such as “moving off the space where the ritual started breaks and halts the ritual”.

Every time you stop casting a ritual (whether it succeeded or failed), it increments the spellbook’s spestudied field; the book will eventually disintegrate after casting it a certain number of times.

Allow all lawful devils (or a random set of lawful devils) to accept a bribe, not just Asmodeus and Baalzebub. They will not vanish completely, but they will turn peaceful.

Demon cartographers (not specified if this would be a new monster species or just the occasional random peaceful monster of an existing species) who offer to sell you scrolls of magic mapping for exorbitant prices.

Split Gehennom into two different branches - Hell, which contains devils and the lawful “demon” lords like Asmodeus, and the Abyss, which contains demons and the chaotic demon lords. Either only one of these generates in a given game, or the player gets a choice of which one to go to in the Valley of the Dead. Alternatively, they’re sequential parts of Gehennom, with the Abyss being deeper.

Add more sources of nausea, particularly in the late game, because it’s an underutilized debuff that only really is relevant early. Proposed sources:

• Certain types of demons or the presence of certain demon lords such as Baalzebub or Juiblex.
• When you are hit with a disease attack but for some reason don’t get deathly sick, or are already deathly sick.
• Stepping over a rotting corpse.
• Some smallish chance every turn you are in a cockatrice nest.

Most of these increased sources of nausea should be subjected to some sort of (low-chance) Constitution saving throw so that characters with better Constitution have an advantage.

Non-chaotic Priests get punished for having demon pets. The penalty is applied upon taming it and periodically from being on the same level as it, so that you can avoid penalties by abandoning it somewhere. (Internally, it should be applied when a tame demon moves; this means if you have multiple demon pets, the penalties stack up faster.)

If you bribe a demon lord with less than 1000 gold pieces, a Wizard-style periodic timer is started, except that every time the timer triggers random demons will be spawned around you. The demon lord itself may return, hostile this time.

All demons are automatically aware of all traps in Gehennom, so they won’t walk into them and trigger them.

When you become caught in a pit, bear trap, or other restraining trap in Gehennom, nearby demons become alerted and aware of your exact location, because they’re the ones who set the traps in the first place.

When a silver item would randomly generate within Gehennom, try to reroll its materials (possibly multiple times) so that it’s less likely to be silver. This is because the inhabitants of Gehennom would likely have tried to get rid of all the local silver. Additionally, demons should never receive silver items in their starting inventory.

Before you first enter the Valley, demons and undead (chosen from the graveyard monster algorithm, though perhaps excluding wraiths) continually spawn in the maze on the right of the Castle and try to path towards the upstairs. Also before it is set, in the Valley, awake demons and undead will try to path to the upstairs if they have nothing better to do.

After the Valley, have a guaranteed special level “The Gates of Hell”. This level design is very clear: “This is hell. These are the gates, and they are closed. You are not wanted here. Go away or perish.” The level is a large cavern, with a massive arc-like fortification across either the left or right side. The gates are implemented with both iron doors and a drawbridge across lava. There is quite a lot of lava, and a lot of demons inside and outside the fortification.

Demonbane, while wielded, warns of demons.

Fiery monsters and possibly some demons get healed by fire traps and will deliberately jump onto them in order to heal up.

Demon and undead pets move reluctantly over blessed items.

Arch-foocubi which do the same seduction as regular foocubi, but the random number they choose has a higher average than a foocubus’ 1-35, so the chance of a bad effect is greater and it’s less effective to boost your own stats. Perhaps rnd(35) + 25. They are also more grabby than regular foocubi, and will steal jewelry if you have insufficient gold.

Demon lord who has no real special abilities, but has a very, very high physical damage output. Or give one of the existing, uninteresting demon lords a high physical damage output.

New demon lord with a fire attack comparable to Asmodeus’ cold attack (this is actually already implemented, but is unused). It seems weird that no demon lords are really associated with fire.

New demon lord who spellcasts, favoring touch of death and summon nasties. However, the only thing it summons and gates in are incubi and succubi.

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

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).