here's an idea...
(I'm being a bit weird here, so bear with me.)
How about something along the lines of Mutant League Sports (a game that was on the old SNES and Genesis), where generally speaking, the rules are the same as "normal" sports, but sometimes, just sometimes people die or are blown to bits or are fried by a fireball...
Just an idea, but it may be fun, especially with the simplicity of the D20 system...
Hehe, I can see it now...
"Kursk, the Barbarian Halfback charges down field, faking left, faking right.... NOOOOO!!! They are going to have a mess to clean up with that one..." - Cuts to Kursk being decimated by a highpowered fireball as the soccer ball goes flying the opposite direction.