Multiple zombie controlers.

[Scoldon]

Satan is the controller. He is a God of the hell, and all that is evil. Later on, Samantha walks into the MPD and becomes the controller. After that, The Doc swiches souls with Sam and controls the zombies. But there's one thing. The dudes on the moon had to open the MPD first. It wasn't active before they opened it. It wasn't active untill a human entered it.

I thought of this: Multiple controllers. When zombies were first created, Satan the Godfather of Evil itself, decided to control the zombies. So this means that the MPD is another way to control the zombies. The other one is to become a God like beign. Element 115 is a Vril-Ya used element. When you shock in 115 in the countdown thingy Satan laufghs and says: Not this time! So when Satan controlls the zombies he doesn't use Element 115. It just reanimates the cells of zombies. When the zombies are controlled trough the MPD, they are controlled by utilizing the 115 in them.