oh, thats fairly simple. did you mean to kill 3 any enemies? or 3 specific types?
my trigger works for both.
[trigger=Kill Counting]QUESTKILLCOUNTER
Events
Unit - A unit Dies
Conditions
(Unit-type of (Dying unit)) Equal to (the type your supposed to kill)
Unit - Killing Unit is a Hero equal to True
Actions
Set QUESTKILLCOUNTER1 = (QUESTKILLCOUNTER1 + 1)(QUESTKILLCOUNTER is a integer variable)
[/trigger]
[trigger=Check Completion]QUESTCOMPLETION
Events
Unit - A unit Dies
Conditions
QUESTKILLCOUNTER1 Equal to 3
Actions
Quest - Display to (All players) the Quest Update message: Completed "Kill Foo...
Quest - Mark (you quest) as Completed
Quest - Mark (your quest) as Completed
[/trigger]