Ok, first, I would like to say that the concept is pretty cool.
But this is too hard in my opinion. Or maybe I just didnt understand what to do at all...
The heros simply don't stop appearing, and they come too fast to me to spawn the ghosts and point them to their bases.
I think that one way to make it easier would be to give some time before the heros start being summoned or maybe make the ghost spawn automatic.