concept 1:
Speculative remix of Splinter. A rat who was mutated by a weird ooze and human DNA from the New York sewers. Splinter would probably be insanely strong, especially being a thick squat rat who can move at the speeds he can and fight toe to toe with humans who are much taller than a 3 or 4 foot tall mutant rat.
concept 2:
More of a Rasta Buddhist using tried and true methods of strength training, capoiera, ninjitsu, gong fu, and USA boxing a la Muhammed Ali.