Flamsterd's flamestrike

Flamsterd's flamestrike was a rare and specialized fire spell that was used either as an offensive spell or a trap.

Effects
The spell created a spiral of fire around a single target. The spell interrupted any spellcasting by the target and caused damage even if the target was magically protected from fire. The spell could strike a target within 10 yards (9 meters) from the caster.

When used as a trap, the spell had to be cast on a piece of metal, such as a coin. The caster then set a series of triggering conditions, similar to magic mouth. These conditions could not involve actions such as entering an area or casting a spell. The trap was immune to magical detection spells, and could only be detected magically if the target was considering an action that was also a triggering condition.

The trap lasted indefinitely until one of the triggering conditions was met. If dispel magic was cast on the trap, the spell was negated. The trap only targeted a single creature, chosen at random. The spell could strike a target within 10 yards (9 meters) from the trap.

Components
In addition to verbal and somatic components, this spell required several material components. The caster needed a pinch of both saltpeter and ash, a small piece of filing of any metal, and a piece of phosphorous.