This seems only doable in JASS, because you have to get the event damage. For the caster not to take damage but still get the event damage, you temporarily set his life very high, test for the event damage, do what the Aphotic Shield does, then set his life back to normal. No one would notice because it is only a split second trigger.
I do not know how to make this spell MUI either because of using a global variable.
I'm on a page about incorrect corrections, and spent the better part of like two hours trying to get someone to understand that -5^2 = -25, not 25, and then that post had comments get reposted because that group is self sustaining, and that person was in turn trying to explain what I just explained to them. And I'm taking that as a victory
I will be AFK for a couple of days you guys hold down the fort while I am gone. I will be checking in on my phone but that will severly limit me. Be back saturday!