If that's the case then I don't think you realize just how bad it could have been. Imagine having an evil twin inside of our head who could use the power of the stellaron just like we can. The worst case during our adventures, would be if they somehow got their own body and took it with them when they left.There are balls that fuse with people and become their evil twins. Generally, but not always, sharing headspace with whoever ate the ball.
This is not a very correct explanation, but it'll suffice. It mostly ends well, except when it doesn't.