I don't know I got a theory on that. MX used to be a good guy just wanting a few answers. Yed Both Yen-sid and ATW told him to leave a few doors unlocked. Chernbog being stuck in the ROD after the Keyblade War, wanting KH which is another door to the world of all worlds and everyone. In a way it's a door to God. He found his puppet in MX telling him about the x-Blade. He told him to make the X-blade to set him free and he would see what he wanted to know. MX had other plans. Use the X-Blade, and take over Chernbog's body and rip open the door of Kingdom Hearts wide open, and take the power of God and play him.