Poison Effect

How do you make a trigger that when someone enters a region, it will slowly eat at their life and kill them? :bgrun:

Event: Timer - Every X seconds

Action: For every unit in (region), set life (life - life*(x%))

Where would I find that action?

It's Unit Group - Pick every unit in region and do action. For the action, do unit - set (life of (picked unit)) to (life of (picked unit))-(life of (picked unit))*10%