Let's put a new spin to it while we wait for corocoro to deliver.

I'll start posting a set for Mew, than someone should reply with a set for Mewtwo that perfectly counters it. Next a perfect counter Mew and so on. We'll always assume perfect knowledge of the opponent's set. Let's see if this series converges or we get caught in a loop.

Of course legit moves and abilities only, but no smogon-like restrictions.
>muh evasion
31 in every IV by default.

A simple one to begin:
Mew @dark gem
- nasty plot
- amnesia
- shadow ball
- roost
nature: modest
EVs: 252/0/0/132/0/124

I'm a shitty player so I'll just watch the battle unfold. Feel free to start from scratch if you want.
EVs