Hey look, it's the only deck I've played so far. I wouldn't say I'm an expert because I'm kind of inexperienced, but I'll do my best to help without just echoing the above poster.
First of all, is this meant to be XY-on? It's marked as standard, so I'm going to judge it as such, but I severely doubt that this deck is going to survive the rotation anyway. Oh well, here we go.
I can't speak for an Empoleon build, but you absolutely need Computer Search, Mew-EX (probably three) and Dimension Valley (definitely four). Computer Search is a huge effect for you, while Dimension Valley lets any of your night marchers attack with a DCE, and Mew + benched Joltik + Valley lets you attack for a single basic energy. Plus Mew can attack with Sky Return, which is occasionally relevant.
Roller Skates is sort of iffy, and Acro Bike only digs two cards deeper while running the risk of forcing you to discard something important. Between Shaymin, your draw supporters and Trainers' Mail, there's no need to play such inconsistent cards. Also, you're running too many 4-ofs - you have so many draw and search options that you can afford to add some more tech to your list, and I doubt you'll ever really need the fourth Muscle Band or Ultra Ball anyway. You probably do need the fourth VS Seeker though. That's an important card.
I'd also disagree with Alian and say you should keep the playset of Compressors. Four copies of the most important card in your deck is not overkill. Yeah, you'll never need to play them all, but you will need to draw into them, and drawing too many is better than not drawing any at all. I'd run five if I could. Besides, there's usually some application for them even when you've pitched all the marchers you need; for example, both of you playing Dimension Valley as your stadium? Every valley past the first is a dead card, get rid of them so you don't draw them later. Night March count is 8 and your opponent doesn't play EXs? Probably won't need those Muscle Bands. Have a Lysandre sitting in your deck somewhere? Sending it to the discard pile to recycle with one of your four VS Seekers later is much more consistent than expecting to just draw into it when you need it - in fact, with Compressor and Seeker, you can pull a Lysandre out of your deck and play it on the same turn. In the lategame, N is being thrown around a lot and topdecks are important? Cut some of the less helpful possible draws out of your deck. And hey, do you really, truly have no use for that fourth Compressor? Get rid of it with your third.
For your supporters, I personally run 4 Sycamore, 2 N, and 2 Lysandre. With so much draw these days, we can afford to go a little bit light on draw supporters, and there's not much reason to run any that aren't Sycamore or N in this deck. 2 Lysandre provides protection from the The Card I Need is Prized blues and assures that you'll almost always have some way to get one into your hand if you find yourself needing one, without taking up too much space in the deck. Remember that Compressor and Seeker exist. Also consider a single Jirachi-EX. It's not necessary now that we have Shaymin and Trainers' Mail, but you might like it.
Uh, and for your basic energy... I don't know, it depends on what's out there for Mew to copy in your metagame. It won't come up in the majority of games, so feel free to experiment with that. Good luck with the deck. If you're going to keep playing it post-rotation, I would warn you that losing Mew is bad news... but if I had to play it, I guess I'd play Shauna over Birch, and throw in some Revives so I can safely keep marchers in the active spot. Then you'd need some way to compensate for DCE being your only way of attacking for one energy. Exp Share to carry over basics, maybe? Robo Substitutes to stall? I don't know, man. See what you can make work.
