Detonation

You inscribe an invisible explosive rune onto an object, surface, or creature. Upon using this ability, declare a condition for the target to detonate. Once the condition is met, you receive a telepathic message and can detonate the rune as a Reaction. If the condition is not fulfilled for an hour after casting, the rune is automatically dispelled.

Upon detonation, each creature within 10 ft. of the blast must roll a Dexterity saving throw. A target takes 12d6 fire damage on a failed save, or half as much damage on a successful one.