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.

Allow for gas clouds of different types (confusion gas, sleep gas, hallucination gas, etc) by passing an additional argument to create_gas_cloud.

Clouds of sleep gas would immediately have a use in Nazgul and orange dragon breath attacks, which are already described as such. They might also be useful for sleeping gas traps, which would emit an actual cloud of sleep gas. Depending on implementation, the sleep gas cloud could have only a chance of inducing sleep rather than always knocking you out, which could make it tactically interesting to navigate/teleport/etc rather than just getting put to sleep and having the cloud gone by the time you wake up.

Potions that boil or shatter (but not freeze) should release a cloud of gas that causes the potion’s vapor effects to creatures caught in the cloud, replacing the existing system where vapor effects can happen at an unclear distance from the site of the potion.

A trap or monster (or possibly change sleeping gas traps or homunculi to this) that causes “sleeping poison”: it starts a very short intrinsic restful sleep timeout, so you don’t fall asleep immediately but have a little time to react.