6. Gill (first appearance: Street Fighter III: New Generation)
Look, say what you want about Gill—he's cheap, he wears a white thong, and he has a serious case of Messiah complex—but he's every bit worthy of being SFIII's final boss. A first in 2D Street Fighter, Gill actually has two sets of sprites, depending on which side of the screen he's facing. Reportedly done to showcase the CPS-3 board, he uses the fire aspect when he's the 1st player, and the water/cold aspect when Gill assumes the 2nd player. Plus he has the most bad-ass Super Art in the game: the Seraphic Wing. This Super Art has him growing six wings reminiscent of the Seraphim in the bible, floating to the center of the screen, uttering “Let me be the one to bless all souls,” before proceeding to shower you with burst of energy. It takes off 75 percent of your life if it hits solo (because of the damage modifier, this can go down to just 30 percent when used in conjunction with a combo), or takes off 20 percent when blocked. (You can't parry it, so don't even try.) That's bad-ass.
On a side note, his secretary, Kolin also has two sprites. Notice her hair is only parted on one side, and this doesn't change.
Image from www.fightersgeneration.com