To get into the art museum, you need to win a master contest by A LOT! To do this in a smart master contest, go to the cave that you had to go through before getting to the elite four and catch a Medicham. It should have mind reader and hi jump kick. Those moves are a combo. Give Medicate some pokeblocks to get it more preliminary hearts, and then, once you're in the contest, use mind reader. The next turn (if no one uses flash or something like that)use hi jump kick. If nobody hurts you, you should get 12 hearts. Do it again, and use a random move last. This, if done right, gets his picture into the art museum. That's how my Medicham got it.