Actually, I wrote a D20 martial arts game drawing from most of SNK (Kim Kaphwan is the MAN) and Capcom (with special love exteneded to Rival Schools/Project Justice) a while ago. Didn't have a lot of time for self-publishing, so I took pieces from it along with a heap of Tekken-inspired goodness and Soul Calibur-style weapons stuff to make the big martial arts expansion we prinited in the Pan-Asian Collective. You might take a look at that, as the Martial artist and Soldier classes play off quite diferently in the ring, and you'll certainly recognize some SFII moves in the feats section

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Baically, I divided moves into 7 levels + Secrets (which are pretty much unique to each character). You made up your own style (distribute points amongst 6 categories of basics- sort of like writing your own martial artist class), picked out moves, or followed one of about 30 styles I pre-addapted from video games, and then you started playing

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Basically, every style gets the following moves when you're finished~
1st level: 5
2nd level: 4
3rd level: 3
4th level: 2
5th level: 1
6th level: 1
7th level: 1
+ 1 wild card (any level).
You could also trade one higher level 'slot' down to bust a lower level up, such as lowering the one 5 slot down to an extra 4 to move a 2 slot up to 3.
With this set up I could map the salient abilites of dozens of different videogame fighters. The possibly supernatural stuff started showing up around 4th level, with energy projectiles at 5th, and signature moves at 7th (Ken's Flaming Dragon Punch, as opposed to the regular dragon punch Ryu uses at 6th level).
To round out high level characters, you can develope 1-3 secret moves. To continue with the Ken example, the "Chain Dragon" multiple dragon punch, the "Dragon Gyser" in-place, no-reach, massive multiple hits move, and the "Super Rolling Hurrican Kick" move would all be secrets. Basically in Capcom terms, if it ate all of your 'power bar' you could expect it to be a secret. I had about 120 moves preped, and rules for making your own, as there was a point-based system for evaluating all aspects of your moves (like reach, damage bonuses, special effects, multiple hit chains, etc.).
Working with Spycraft, I'd use the 2 half/1 full action per round system, and fluid initiative, but d20 does really lend itself to such conversions - Reflex saves vs. Sweeps, Fort saves vs. staggering blows, Will saves to produce some of the more mystical and flashy effects. Honestly, it wouldn't be that hard to do

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