If you are going to use an update loop, use one of the single registration variants so that you don't get stuck with an infinite loop bloating someone's save cause they removed the mod at the wrong time. But yeah, you can use an update loop to damage the caster. You can also use that same location to apply a visual FX, see Play. So for example, I can use RegisterForSingleUpdate on spell start as well as in the OnUpdate function for this?