about the function..
the call function "stores" the uid number in parameter0 from the event it calls the function,then in the executed function itself it picks the "sprite" with uid(parameter0)
looking at the capx, for a newly created creep you should
make the same function as "creepPickDestination" without the creep-picking condition
name it "newCreepPickDestination"
on creep created , call "newCreepPickDestination"