So the word 'Tenacity' means that you don't go down easy, as far as I know. You hang on til the bitter end. And I can... sort of see how that fits what it does right now, but what if it was changed to better suit the word that describes it (Also this is a nerf to MK, btw).
Tenacity - If hero's health falls below 50%, they become immune to Crits and 25% to get an extra attack and the end of every round.
Basically, combine Tenacity and Wushu to make this one passive (meaning remove Wushu), and nerf both to function only when he's under half health. It better suits the description of the ability, and nerfs MK to not be so OP.
While we're at it, perhaps what Wushu was could be given to Sifu because it suits his character better. Ya know, how Monks undergo intense training to be able to move their vital organs around inside their bodies so they're never hit in a vital spot (basically what a critical hit is, anyways).