You only need to do a fatality, a stage fatality, and a babality to get it. I thought it had to be by the same person but the first time I did Kang's babality it popped up and that was the first finisher of his I'd done.
just one of the 3 different "-alities" and that's all you've gotta do. i myself got it while going through the challenge tower. some challenges prompted me to finish the round with an "-ality" and it was that simple