Change the atlatl into a launcher that throws spears. This means that Xiuhcoatl is no longer a weapon in its own right. Re-buff it by making it give fire damage to all spears thrown from it, and also reduce the weight by half of all spears in main inventory, or make them weigh 10 like daggers.
Attacking a dead tree with a weapon of fire, or an artifact with fire damage, will burn up the tree.
The game should not assume heroes all carry an unlimited invisible box of matches to light candles and lamps with. Doing that should require a fire source, whether that is Fire Brand, lava, a fire trap, the wand of fire, the fireball spell, or an already lit candle, lamp, or potion of oil. There could also be a new “lighter” tool which enables you to light things, but can get lost or run out of charges.
You can pour a potion of oil over yourself to temporarily block any invisibility for 200 turns. While oiled, you take double damage from any fire source, and you can slip through boulders diagonally without worrying about how much stuff you’re carrying.
Grass terrain, rendered as a green period or comma. It could have the following properties:
New type of terrain, “fire terrain”, a square that is on fire. It displays as an orange period. (If this will be too nasty to people who play with color off, the glyph should perhaps be changed.)
Fire damage is amplified for any creature who has greased fingers or equipment.
Hellfire from monster casting, being inspired by Ghost Rider, should in addition to ignoring fire resistance slow the player down, since it does spiritual damage that reduces the victim’s will to act.
Livelog when a Caveperson player creates fire for the first time.
A tree hit by a fire ray or explosion should instantly incinerate, provided it’s not marked non-diggable (petrified). Likewise, a tree hit by a disintegration blast should disintegrate.
Whenever a fire attack “partially vaporizes” a water-based creature such as an elemental, there is a chance a steam vortex will be spawned adjacent to it.
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.
When a pool of raw sewage boils away, it creates a poison gas cloud over that space.
When you hit a tree with fire from any source, it can turn into a burning tree (#). This burns for a few hundred turns before burning out and turning into normal floor. While on fire it acts as a light source of radius 9, and deals fire damage to anything adjacent each turn and occasionally to anything within a radius of 3. Come to think of it, there could also be a “bonfire” terrain using the same glyph.
Attacks that light things on fire also light things on the target square on fire.
Using fire on the water on the Plane of Water boils the water away and opens up air space, but spawns in steam vortices.
Lighting a web on fire will burn it away, and also spread to any adjacent webs and burn through them. Monsters on squares containing burning webs take a smallish amount of fire damage.
Fire and Frost Brand can be invoked for powerful fire and cold bolts.
Non-weapon artifact which, when carried, adds bonus fire damage to all of your physical attacks, regardless of what you’re using to make the attack.
When a potion of oil gets hit by fire, it ignites and explodes.
Greased scrolls and spellbooks, if they catch on fire, burn up and deal additional damage.
Fire bolts light potions of oil on the ground that the bolt is zapped over, and cold bolts snuff them.
Wielding and hitting enemies with a pyrolisk corpse deals fire damage.
Give Lord Surtur fire attacks, since he doesn’t actually use any.
When the hero observes a fox take fire damage, print a YAFM about Mozilla Firefox or automatically name the fox “Mozilla”.
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.
Balrogs have a fire attack.
Fire/flame nymph, n, which normally only spawn in Gehennom (or possibly near lava not in Gehennom) and are noticeably stronger than other nymphs. Have two steal attacks which burn any items stolen, and also a fire attack. Potentially a passive fire attack as well. They also explode into fire when killed.
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.
If a cloak is on top of an item pile, it will protect anything underneath it from burning up in a fire blast on that space (though the cloak itself might burn).
A troll killed by fiery or acidic means (including Fire Brand) cannot revive.
Greased items that get exposed to fire become flaming for a certain number of turns afterwards (and then the grease is gone).
You can light a greased sword on fire. Attacks with it will deal fire damage for a few turns until it burns out.
Make being on fire a status effect, which deals damage over time. (Other obvious things to make into damage-over-time effects: poison, bleeding/internal damage.)
Candle additions:
You take fire damage from standing next to lava, levitating or flying over it, or walking on it. Damage from standing next to it is (number of adjacent tiles)d8, whereas being over or on lava has rather higher damage. Fire resistance does not prevent this damage completely.
