It's only in black and white, mewtwo can learn psystrike and you can't get a mewtwo in those games.
Get any Mewtwo to lv 100 in black or white. Bring it to black and whit through poke transfer and get it to lv. 100. In order to get Mewtwo go to cerulean cave to the center and catch it in hgss. Get it to lv 99, bring it to b or w and rare candy and it will learn it.
Poketransfer it by the facility after you defeat N and the Elite4 and then raise it to level 100.I have a really good strategy.Keep going across the Skyarrow bridge while you have a Pokemon in the daycare because when you have finished,you can run on the second to outside tube of the battle railway.sellotape the B and the down button.Leave it in the charge and go to sleep.Also if you want to gain EV`s,fully EV train your Pokemon before you apply anything here.