Mew

If I were paid for all of Mew's movesets, I wouldn't be able to spend it all in a hundred lifetimes. Mew learns every single TM in all of Pokemon, and thus, its versatility is what all Pokemon wish they could have. Except Smeargle, that is.

However, Mew can't really come in on anything without taking a decent chunk out of its health. It wishes it had more resistances to things other than Psychic- and Fighting-type attacks. In the sweeping department, Mew is also outclassed by Mewtwo, who is faster and more powerful. Still, it's Mew's versatility that makes it stand out, so its advantages over other Ubers should be exploited. Mew also has the ability to Baton Pass whatever boosts you see fit, which is truly an extraordinary ability, one that should never be overlooked.