|This spell attempts to convert all nearby poison into liquid flame, burning poisoned creatures from within. It is very effective against innately poisonous creatures. The caster is not affected.|
Ignite Poison is a level 5 Fire Magic/Transmutations spell which causes all nearby poisonous things in line of sight to burst into flames (excluding the caster). Any monster which leaves a poisonous corpse, is poisoned, or (in some cases) has a poisonous attack takes fire damage (and is cured of any poison in its system). Ignoring the player's inventory, all poisonous corpses and chunks, all potions of poison, strong poison, or degeneration, all poisonous ammo, and all poison or noxious clouds burst into flame clouds.
Ignite Flame deals unavoidable heavy fire damage to every susceptible thing in sight. This makes it extremely effective in certain situations, such as killer bee or kobold vaults, or pretty much any part of the Spider's Nest or Snake Pit. Just make sure to watch your MP, avoid overconfidence, and be aware that there are dangerous invisible opponents in the Spider's Nest which will not be affected unless you can see invisible. While these are obvious areas for its use, you can increase its deadliness in other areas with a little creativity.
Ignite Flame works great when used together with Mephitic Cloud; the noxious clouds generated by the former spell turn into clouds of fire. First confuse them with Mephitic Cloud, possibly casting it a few times to cover a larger area, then (once the monsters are confused) cast Ignite Poison and let the poor guys stumble through the flames. Casting Ignite Poison after casting Poisonous Cloud creates the "fire version" of Freezing Cloud.
Also note that monsters which are immune to Mephitic Cloud will happily walk through its noxious clouds to reach you. If you cast Ignite Poison at the right moment you can blast them as well.
It is possible to throw a chunk of poisonous meat and ignite it afterwards to place a cloud of fire at a certain location (f.e. under a monster).
Although no monsters are able to cast Ignite Poison, there is an equivalent spell (Localized Ignite Poison) which has the same effect but can only target one opponent. The following monsters can cast Localized Ignite Poison:
Ignite Poison used to be an amazingly painful way to eliminate poison from one's own system, but as of 0.8 it no longer affects the caster or his inventory.