I was trying to get the warp zone in 4-7x.. I saw a glitched Bandage Girl then decided to finish the level since I didn't have the glitched level yet.
After I finished the glitched level, I went back to the level selection but instead appearing on 4-7x. Meat Boy was in the place where the MMMMMM warp zone would be. So I was able to play MMMMMM warp zone without unlocking it.