Yeah I am thinking this as well. I think Dr. Satan does some crazy shit to "Earl" and then he becomes the crazy ass pick axe weilding freak at the ending.

Thats what I think happend.

yeah because if you remember when they showed "earl" burning tiny he looks a little different and then when he is showed at the ending he looks more savage...I am hoping Rob explains more about all this in the sequel or even future sequels for that matter..