Specific unit event - Takes Damage

What I want to know is, how do I get the unit that took the damage in my actions and conditions section? Would that be Triggering Unit? Also, how do I remove events from a trigger. Somebody(I think it was Anitarf) told me that you needed JASS to do this, which I don't know much of, but it would be nice to be able to remove all the Events that get added when units enter the map. Thanks for the help.

yes Triggering Unit refers to the unit that took damage. It event clearly says so if you look at the tooltip for it. :)
about the other part, i dont really know :>

Actually, I think you can't remove events, that's why I suggested using JASS, because there you can just make new triggers (instead of adding events to an existing trigger) whenever a unit enters the game and destroy the triggers when the unit leaves play.