He didn't post a tutorial, but you clearly paid no attention to the King of Fighters XII nor their
gallery For raizel or whatever his name was and kratos, he seem to have animated 3d models of them with a toon shader, then reduced their colors to 256, fixed the palette to be mugen compatible, then made a character of them. Orchid on the other hand seems to have a bit of pixel work added in on her.
He used blender for animation (as he says that he uses
Blender on his site but with no pictures of what he did in it.)
The thing I want to know is where did the models come from
. They seem to be rips from games, but I don't really know of a 3d killer instinct.