Really? Zoroark stands out a lot for me, but there may not be an objective truth here. Still, Mewtwo is supposed to be that one special pokemon. He's been created in a lab. He's this one guy among the other 149 (in case you decide to pick on Jynx :P). Even then, the style feels more similar to me.
I mean, it's kind of natural that designs made at about the same time by the same people tend to look more alike.