**aggron can learn aqua tail in X**
but as you said: only if you trade him from BW2 to X&Y, so go to the move tutor in BW2, have him learn aqua tail, deposit him in the pokebank, switch your game to Pokemon X and get aqua tail aggron. just a little nitpick and the reason I answered this question although it had already got an answer: I wouldn't recommend power up punch for aggron. teach him stealth rock if its mega-or head smash if its normal aggron to make use of its ability