Convert the sleeping gas trap to just “gas trap”, and make it scale based on the difficulty. Each individual trap releases a single type of gas; which type is partially dependent on the level difficulty. At low levels, they all emit sleeping gas like normal. At higher levels, they emit stunning hallucination gas like container traps, clouds of poison gas, and maybe even nastier gases that reduce speed or miasmas that cause illness.

Pale jelly, a j or j that has an engulf attack that causes illness and a difficulty rating appropriate to that. Some may be found on Juiblex’s level.

Apples (may) cure illness when eaten when blessed. However, their doctor-repelling power is increased to the point that Healers take damage when eating them or suffer some other negative effects, and hitting a Healer player monster with an apple scares them.

Deathly illness should produce warning messages at various points as it ticks down towards fatality, similar to how most other timed instadeaths work. This would, among other benefits, allow players to set those messages as MSGTYPE=stop.

If you get hit with multiple illness attacks in the same turn, the second one functions like Famine’s attack, draining your nutrition, rather than speeding up your delayed instadeath.

Wielding a copper object or wearing copper armor protects against an otherwise successful disease attack some of the time, because copper is antibacterial.

Ants (or locusts, if implemented) can eat food off the ground, and they create more of themselves when they do, proportional to the nutrition consumed. They can also eat food out of the inventory of something they are attacking, and if the target is carrying food in a bag, they can reach into the bag and either eat the food there or spill it out on the ground. Locusts that can’t find any food to eat could inflict illness with their bite instead. They could also eat grass terrain, if implemented (turning it into normal floor) and multiply that way.

Maybe, to avoid the problem of how unchecked gremlin multiplication creates a bunch of low-HP, one-shottable gremlins, locusts will increase their maximum HP by eating if their own maxHP is below some threshold. (Then they’ll split again by eating more after getting over the threshold.)

Change the sickness instadeath to a HP-based form of damage, since it is very obscure about how long you have left to live and can be drastically reduced.

• Instead of a death timer, apply a penalty to HP regeneration rate, with this penalty being variable and slowly decreasing as you recover from the sickness. This is nice because it allows for monsters to have a sickness attack in the early game.
• This penalty can be large enough to make your regeneration rate negative.
• Getting hit by a sickness attack while already Ill not only increases the severity/duration of your illness, it deals some extra damage proportional to the severity of the sickness.
• Severe enough sickness only partially times out - you will need to take some actual self-healing action like quaffing healing potions, praying, casting cure sickness, applying a unicorn horn, etc. to be completely cured.
• Unicorn horns no longer cure the entire illness all at once - they will only reduce the severity (which might cure the illness all at once if it’s mild).
• Being sick for a long time may cause vomiting, Con loss, Str loss, and occasionally hallucinations.
• Sickness will eventually go away on its own if it’s not bad. Maybe look to FIQHack zombification disease for specific mechanics for how this could work.