...I was looking at the sprites, and they both have mohawks, but Marshtomp's is a darker blue and he has fins on either side.
He could be the final evolution, actually, since he's wearing orange wristbands.
T'be honest, it would've been a lot easier if he'd just styled his hair a bit more. Or made a tail of some sort. Or worn chaps, or...something. This one really is hard to recognize, since Mudkip is so famous and its evolutions are so ignored because of how fugly they are.