Ice devils have a “hellfrost” attack that can damage you even when you have cold resistance (though possibly not if you have extrinsic cold resistance).
Hitting a tree with sufficient cold damage makes it explode. The explosion type could be either physical, like a gas spore, or cold itself (which could possibly set off a chain reaction causing other trees to explode).
If you attempt to move into a ghost’s space (either if it’s invisible and unseen by you, or by m-moving, not by moving normally towards it when you know something’s there which would still be an attack), you successfully move there, displace the ghost to an adjacent space, and take some damage from creepily passing through a ghost. If this is implemented in an extra evil way, this could be cold damage that destroys potions.
Gelatinous ice cubes, which work mostly like gelatinous cubes but also have a cold attack.
If you die to overwhelming cold damage (on the order of 3-4 times your current HP, for instance from Asmodeus’s cold attack), you leave behind a frozen statue (made of ice?) instead of a corpse.
For variants with a “frozen in ice” status effect, this effect will be randomly inflicted a small fraction of the time on water-ish monsters (water elemental, water nymph, water troll) that get hit with cold damage.
The corpses of monsters killed by cold effects take longer to rot. (Maybe they should also be fresh for sacrifice longer than usual.)
Fountains can be frozen, creating a silver or cyan “frozen fountain”. These can’t be dipped into or quaffed. They appear in ice-themed levels.
Fire and frost horns, rather than shooting a bouncable ray of fire or cold, cause a powerful area fire or frost effect centered on you. The intensity diminishes the farther away from you it gets, but it hits every single creature in its fairly large radius (except you).
This effect could also freeze water and lava or evaporate pools in the radius of effect as well.
Freezing a fountain does something. All the following have been suggested:
Fire and Frost Brand can be invoked for powerful fire and cold bolts.
Fire bolts light potions of oil on the ground that the bolt is zapped over, and cold bolts snuff them.
The proper way to make late-game elemental damage matter is to give late-game enemies elemental attacks with large enough damage to matter, which don’t care about reflection.
Intrinsic cold resistance only halves damage from Asmodeus’ cold attack. Only extrinsic cold resistance protects against it fully (or cuts it to 1/4?).
Cold rays are colored light blue, to be distinct from lightning.
Hitting a fountain with a ray of cold or cold blast freezes and breaks it, creating frozen pools in the area.
Asmodeus’ cold attack can freeze potions in containers.
Frost lamp, a tool which gives out a radius 3 cold aura. Water and lava within the radius freeze and then revert once out of the radius. Fiery monsters take damage from being in the radius. Eventually runs out and has to be recharged.
