I thought that the head was too wide and that some of the shading wasn't in-style. So I made some minor edits (head is two pixels skinnier, changed some shading on the belly, legs, and arms). I also think the yellow is too dull and the pink for his nose is too bright, but I didn't attempt to change the pallette yet.
(on the left of the two Warios)
(on the left of the two Warios)