Demon Fire in Heroes 4

When thrown at a target it causes a 3x3 yard explosion of flames (same as the Fireball spell) around a target within the line of sight of the caster, doing fire damage to all targets within its blast.

Alchemists claim that they are the inventors of Demon Fire. Even if an alchemist had created it, many believe that he must've been a demon in disguise to come up with such an evil substance.