Pokémon X and Pokémon Y

Is that how it works? I thought it worked like Ditto, where it only worked for the duration of the battle.

Then again, I don't really know anything about Pokemon post-Gen I.

It is. It also learns Sketch again every ten levels (at 10, 20, 30,so on). It can learn literally any move in the game. Shame its stats are absolutely terrible though.