Well, you could always have a trigger that, when the spell is used, a trigger puts a chaos ability on the unit, morphing it into a unit that has the [detonate] spell from wisps. Then, have the spell put a buff on enemies. Have that buff last 1 second and drain an amount of life equal to the damage you want the spell to deal. This would use less triggers, if that's what you're wanting, but I am new to mapping, so I'm not sure just how effective that would be.