5. Clayfighter 63 1/3 | Nintendo 64 | 1997
How and why are you fighting Santa? Because Clayfighter has always been such a 'hilarious', 'quirky' and no doubt quantifiably 'wacky' series, and because its mascot character is a snowman, it was crushingly inevitable that Santa would eventually appear. And in the third game he did. In an explosion of pioneering obviousness he was conceived and realised as a walking fat joke, fighting in a pseudo-sumo fashion and with his belly out because "LOL LOOK SANTA IS FAT!". Oh, and his finishing move is to butt-slam himself on top of his stunned enemy, wedge them up his crack, and fart out their bones. Keep it classy, Clayfighter.
The storyline reason for fighting him? Sumo Santa is sort of an evil version of Santa, and a rival of Bad Mr. Frosty. He's been exiled to the tropical Klaymodo Island since Frosty took control of the North Pole and he now wants it back. So, you know, fighting.
Is he the real Santa? Probably not. Though it' s all a bit vague. Let's say no, because the real Santa couldn't possibly be that crap.