Have you grabbed anything from White Forest yet? It's post-E4, eastern Unova. I can give you a Vullaby, but want to get my legendaries cloned before giving any away (I have the entire Dex except for Meloetta and Genesect, the latter coming in October).
If you keep any of those on your final Elite 4 team, I will be surprised. All I will say is this: make sure you get a Scraggy and EV train it for Attack, because you are going to be happy you did come the E4.
I also suggest acquiring a Zorua Egg (or already hatched) via trade. I have done so and took it to the Battle Subway yesterday as a fully evolved Zoroark. For the first 13 battles, it was unstoppable in the first slot and at times the second slot (dropping due to fatigue in the third battle). I then lost in the first battle in the 14th fight, and it led to my losing the match in the end.
So yes, definitely get one of them. The Dark will come in handy in the Psychic battle of the E4.