I wouldn't add anything this close to Nats, for you may break the deck. I cannot help you add anything for I do not know your list, nor do I need it. However, I can supply you with a decent strategy:
With you're deck Tornadus
really lolz at your Groudon; It takes all of your most powerful attack to three-shot it while two-shotting you.
Hm. Mewtwo can be a hassle with this deck, but if you can keep the healing coming, then you are golden. They have to have six energy on their Mewtwo through all of your BanHammahs and Lost Removers to one shot a Groudon with three energy on it, not counting if he has an Eviolite on it.
Expect them to fight with Tornado all game. Sadly, this is unavoidable. They will swarm Tornadus on you and you'll have to manually fight through them.
But... There is one they fear. In their tongue, is Catcherkiin, TrainerBorn! Catch-er-Celebi! *Skyrim music plays*
Sadly, they will bench just so many Celebi (Usually at the start of the game as their first basics) and then you will be stuck with Tornadus. What you can do is Catcher up Smeargles and KO 'em. But this, too, will run out soon enough.