Trigger for no player owned units in region

[Necromund]

Hi there, basically needing help to cause the following effect:

I want a unit to be within a certain range of a boss unit or else it will cause a huge explosion (ie - learn custom flamestrike and nuke you), so you have to hug it. I figured the best way to do that would be with something like regions and picking all units, but i cant seem to find the desired trigger effect from that.

Think 4 horsemen fight from WoW, im basically doing a version of that.
http://www.wowwiki.com/Four_Horsemen

If anyone has any advice that would be much appreciated, thanks in advance

 

[Nichilus]

Use a periodic time event. Make that trigger check the distance between caster and target. Or if you need any unit (in case there are multiple units), then make a unit group selection and select units within certain radius that are alive and are enemies of the boss. If the unit group is empty, no units were picked and so you punish people.