[Varyon]

It's an Advantage rather than a skill, but "Natural Weapons" (Pyramid #3/65) can be good, here. That can get you Ken's flaming fist (if you've made his shoryuken into a Technique, requiring a specific Technique to make use of a Natural Weapon is probably worth -10% or so), Dhalsim's yoga fire (one of the examples is dragon fire IIRC), or possibly even Bison's* Psycho Crusher. That last you'd need to add some Limitations to only be usable with a Slam, arguably. Also, hadouken (flaming and regular - use Burning for the former, Crushing for the latter) and similar are readily supported.

*Or Balrog, depending on which version you're playing. In the Japanese version, the boxer is M. Bison and the evil military guy is Balrog; the former is a pretty obvious reference to Mike Tyson, and Capcom USA - fearing lawsuit - simply swapped the two characters' names. Or so I've heard.