Your random new lines scare me.
Make something based off of immolation, or if you want something timed, a simple trigger with A Unit Starts the Effects of an Ability, condition is the spell's name, and the action is a loop with a one second wait and a unit group - pick all units in 200 radius around Casting Unit and Damage them.
That wont work for several reasons, including Casting Unit not picking up the right unit after waits, as well as leaking majorly.. but that is the idea of how to start it.