I don't think Rifftrax has done many/any kung fu movies before, but it's a genre as ripe for mockery as any. Duel to the Death is an especially cheesy example from the 80s with a cliched noble China vs. evil Japan plot; it's at its silliest during the many scenes of inexplicable ninja magic, such as the underground burrowing ninjas, the talking/exploding severed ninja head, or the ninjas that Voltron into a giant naked woman. And best of all, the titular duel at the end has plenty of Holy Grail limb severing but NO actual DEATH. I feel like it even has a really hilaribad English dub. Hopefully the foreign nature wouldn't make it impossible to license for Rifftrax.