I'm testing Empoleon/Donphan right now, and it seems to be working pretty smoothly. The deck is a bit touchy, so you have to play it right. I currently run 4-4 Donphan and 4-1-4 Empoleon with a Dual Ball/Communication engine. I'm tempted to switch over to Pokemon Collector, though, because I tend to have problems filling the bench when Empoleon gets out. That, however, is when the deck really shines. After the first Empoleon hits the field, the deck just takes off.
In addition, the other thing to look out for is that the deck is matchup-sensitive. I know every deck is matchup-sensitive, but your strategy for different opponents can seem like you're playing a completely different deck. Against ZekEels, you swarm Donphans. They'll eventually drop Tornadus EX/MewtwoEX/Tornadus, but you have to ignore them and keep on Catchering for KO's. You'll start to get ahead on the prize race, getting OHKO on {L} pokemon. Eventually they'll stop dropping them, and that's when you break out Empoleons to go after the non-{L} EX's they've dropped. Just make absolutely sure that you've destroyed every single Eelektrik in sight before you do.
My favorite to play against are {D} decks, because you swarm everything. Max out on Donphans, but don't stop there and just keep on setting up Empoleons, too. It's really a pretty easy matchup, because you take a OHKO every turn compared to their 2HKO's and occasional OHKO with Zoroark. However, if they have enough benched pokemon to OHKO you with Zoroark, that means Empoleon will be doing maximum damage.
CMT is a pretty good matchup, too. They don't run any {L}, so you just swarm Empoleons and win the prize race. (Seems like I'm saying that a lot.) Same goes for Terrakion. You can OHKO a Terrakion with a pluspower if they have a full bench. If they keep their bench small you 2HKO them and use Max Potion to stay ahead on the prize race.