Force unit to use ability

I want a trigger than, when a unit's hit points is less than or equal to 10%, it should stop, being unable to move, wait 2-3 seconds, then unleash a nova-like spell that damages everything around him, then add a 30-60 second cooldown to that so he doesnt chain that ability when under 10% hit points.

I've almost managed it but the editor didn't let me use a 'Unit - Damage Area' action... So I'd prefer some other thing...

Please help :)

P.S. I want the skill(trigger) to be shown as a passive skill at X3, Y2, and when this trigger has been run, the cooldown clock should start over the icon.

Although, the passive thing is not so important, the trigger itself is the most important thing atm.

here, i attached the map i put all the triggers in, change it if u want to, hope it helps