When Mikey sent Casey back in time Leo thought it destroyed Mikey to open the portal. it only destroyed his physical form. in one last desperate attempt to save his brother Mikey sent Leo back in time, but Mikey didn't realize how much his physical form held back his powers. He sent Leo back just a bit too far... like before the brothers were even mutated. Whoops. Picture is not my work and is temporary until I can draw a more appropriate piece.