Street Fighter 3: Third Strike Online Edition. I love fighting games. I am in that most dangerous position of knowing a lot about fighting games but not having enough time to back it up. I know about kara-throwing, and a bunch of other weird sub-systems in Third Strike. Unfortunately, I still have problems timing my post-karakusa fierce-to-hayate combos or parrying Chun-Li's Houyoku-Sen super-art. Still, this is a really fun game with some seriously amazing 2-D sprite-work and an excellent cast of characters.
The design I used is based around Gill, the final boss. He's a jerk. If you try wear down his life while he has a full super meter, he resurrects himself. It's pretty infuriating.