1. Use a variable to make the trigger fire.
Script
fireTrig1=true
Trigger
Condition: fireTrig1
2. Almost never use ==. Certainly not with numbers - it's not reliable. Some screwup could cause the number to be 2.00001 as far as the computer is concerned. Also, when counting the units in a group, you can get long (several minute) delays before the trigger fires. Use an alive command to make the group leader (and therefore the game) aware of the number of loons in the group. You want
"alive _x" count units grp1 < 1
You must put in place a mechanism to cope with last few loons in the group fleeing to the far side of the island and becoming unfindable and therefore unkillable.
Oh, and
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