ON_DEATH <ThingID> [count]
This will cause a trigger to not activate until all things of <ThingID> are killed or removed from the map.
<ThingID> can be the name or number from THINGS.DDF, like IMP or 3001.
The optional [count] is a numerical value which causes a counter based on how many <ThingID> are left to kill. If used, the values should be greatest to lowest as you read down your script.
START_MAP MAP01 RADIUS_TRIGGER 0 0 -1 ON_DEATH IMP 1 // runs when only 1 Imp is left alive TIP "Only 1 Imp left!" END_RADIUS_TRIGGER RADIUS_TRIGGER 0 0 -1 // since we don't specify a count, ALL imps must be killed ON_DEATH IMP TIP "All Imps killed!" END_RADIUS_TRIGGER END_MAP