If you've seen my Heracross' movepool, you'll know it's actually a type disadvantage.
Start with a Fury Attack, but if any hit destroys a clone, then redirect the next hit to the next possible Volcarona (obviously if you hit the real one on your first try, keep pounding on it). Then, if the clones have been destroyed, break the substitute with a Smack Down. Finish with a Stone Edge.