1. Use Starts the effect of an ability instead. It works more accurately.
2. Try using a Pick Every Unit loop to choose the units in the area, then damage them individually.
3. You should begin learning about memory leaks.
Remove the Wait.
Changed event used to Starts an effect of an ability.
And according to your trigger, this works only if your spell is Level 1.
Then try again.
Unit Group - Pick every unit in (Units within 512.00 of (Center of (Playable map area)) matching (((Owner of (Matching unit)) is an enemy of (Owner of (Triggering unit))) Equal to True)) and do (Actions)
Loop - Actions
There is no picked unit until you are inside the unit group loop, when setting the group you need to use matching unit.
I do know this - xenforo dropped the ball by not keeping the vbulletin reputation comments as a feature. The loss of the Reputation comments data when we switched to Xenforo really was the death knell for the site when it came to all the users that left. I know I missed it so much and I got way less interested in the site when that feature was gone and I run the site.
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