A really good facsimile of Mewtwo is indeed possible on Smackdown vs RAW 2011's CAW engine. However, to achieve the level of accuracy I've attained, you'd need to hack nearly everything (from his physical appearance down to his moveset--even his two created finishers are hacked!).
As such, it would be far too complicated for me to explain in detail how to build your own Mewtwo CAW exactly matching mine.
I can, however, give you some idea WHAT went into my creation.
1. Deletion of underwear/bra layers (that's right--I started with a DIVA template, due to it giving a more accurate body curvature)
2. Replacement of eyebrow, eyelash, lips and teeth layers with clothing items/accessories (cat's paw gloves, horns, female top and mask)
3. Hacked transparency of above clothing items (except horns)
4. Hacked logos sculpted into tail-shaped silhouette on Mewtwo's backside
5. Extensively hacked chain-grapple moveset (replacing mundane chain-grapple moves with classic finishers, such as Stunner, etc.)
6. Hacked created finishers (normally incompatible animations spliced together, as well as given maximized damage)
7. Hacked attributes (all 7 in-game-editable attributes maximized at 100; eighth "hidden" attribute maximized at 255)
8. Hacked abilities (Hammer Throw, Resilience, Durability, Kip-up, Outside Dives, Springboard Dives, Fired Up and Leverage Pin)
Mewtwo's two created finishers are The Mewtron Bomb (military press to dragon wings impact) and The E.M.P. (military press to suplex impact 3).
Mewtwo has a sort of "twin sibling" on Smackdown, named Shiny Mewtwo (because he IS a Shiny Mewtwo). Shiny's moveset is different than Mewtwo's, in that it replaces many of Mewtwo's combo-based moves with stronger, single-hit moves that have a high bleeding potential.