Pokémon X and Pokémon Y

 Spoiler

I'm thinking you can Spite all of his Recover away, then False Swipe + Spore for the win.

I REAAAAAAAAAAAAAALLY want my Parasect from Black 2 now :<. It made catching things so easy.

I guess I can wait until December... not like I need Mewtwo right away.

 Spoiler

I used Poke Balls. Took about 20 tries, using my Yveltal to stop him from doing much but spam Barrier/Recover. Oblivion Wing to heal any lost HP and deal some damage if Mewtwo used Recover. A few weeks ago when I was working on Black 2, I checked a capture rate calculator and found that there is no real bonus for using Ultra Balls over Poke Balls, or any need to drop a Pokemon down to 1 HP, as 10% and 1% resulted in the same chance of capture, or very close to it. Dusk Balls were something like 4x more likely than Poke Balls though.