Couldn't I do some sort of hard cap on how many of the unit can be on the map. And since the trigger thats run after they choose a hero creates the hero they choose it should in theory return back an error if it trys to fire off a 2nd or 3rd time?
Something like condition if unit = hero1 >1 return false?
I swear I had a setup in the past that worked something like that I just can't remember how I did it.
And by the way thanks for throwing ideas out