Fetis=Dr Fetis When His Glass Shatters
Larry=The Wormy Guy
C.H.A.D=Cute Huge And Deadly
C.S.A.F=Cute Small And Friendly
Dr Fetis Button=His Evil Button
Little Slugger=The Saw Thing With Feet And A Cockpit
Meat Ninja=Meat Boy But A Ninja
Little Horn=Multiple Dead Meat Boys Mixed To A Giant Monster

want more information or more ideas?
here is the wiki link.
http://supermeatboy.wikia.com/wiki/Super_Meat_Boy_Wiki