Also, no discussion of Bruce Lee and MMA is complete without this famous scene:
New idea: in Dungeons & Dragons, levels are just how big you are.
It's literally just a weight class. so by the time you're 20th level, you grown to 8 ft tall and weigh 700 lb.
I don't how I feel about that as a class option. I am picturing something very animated. But I had an idea when I was doing wuxia and kung fu campaigns, that you could make each school of martial arts a class and allow for fairly heavy class dipping mechanically (but with very in game restrictions----like you need to convince a particular master to teach you, join the martial arts school you want to learn from, or steal a manual). I thought that might work good for kung fu and wuxia movies. It is just a matter of how finely you want to categorize styles. Another way I thought of doing it was with specific techniques. So you could take five levels of the Eighteen Subdoing Palms Technique, then one level of Jiu Yin White Bone Claw, and three levels of Emei Swordplay. Some techniques might only have 1 or 2 levels, some might go higher.
most Wrestling inspired games use this route of having class = style eg “Aerial, Brawler, Technical and Power” and then build using skills and manoeuvres.
Weight class is also very important in Wrestling too, so maybe Level adjustment is in order