Onix /w body + Steelix Prime. Onix's body seems to stack, so you can drop a Special metal to Steelix and heal 30. It has staying power until...
Entei&Raikou LEGEND come and OHKO it away. They will also be sweeping Claydols and Uxies in the BRs near you. They seem like a viable tech in something like Luxmane, or even in DialgaChomp. Detonation Swirl can own so many decks that it's not even funny.
I'm curious as they always make some rogue potential to every Octillery. This one is no exception. Sniping + hiding? Double Mimes while you snipe anything that's charging up in your opponent's bench? I see it being played, although I'm not sure if it will be competitive enough in the heavy sniping/gusting environment. If teching Politoad, this may actually use Spiritomb without fear for them getting Chatterlocked, but the damage potential is just a bit too low. Unlike...
Kingdra Prime, that will have the built-in snipe in it's body. I already wrote something about Kingdra Prime lock, and it's attack isn't half-bad either. 60 for 1? Sounds donk-a-licious! The downside is that the fire pokémon will be reducing it's damage, although Entei&Raikou seems like the only capable one in this set. Most fire decks are energy intensive, so Kingdra would usually beat them easily if teching LA Kingdra...
..and then there's the energy intensive deck's new tech, Shaymin. This will be crowning Tangrowth as the second best grass deck around (Yeah, well, Jumpluff is actually playable!?) with it's power. Even the attack will support Tangrowth due to the healing capability. Too bad Tangrowth GE is rotating out, I was seeing something awesome there for a moment.
Too bad there's no cards that will actually affect the metagame. Kingdra Prime will do the same to Kindgra what AR did to Gengar, change the deck's focus a bit and make Kingdra LA mostly a tech. Tyranitar prime - well, the only spread usable will be spread of 80 to every pokémon with power by Entei&Raikou. Tyranitar has some staying power, though, but the speed is lacking in the 2HKO environment, and the effects of it's attacks aren't that great. Jirachi will be trying to accelerate some decks like Giratina or GG, but is a bit flippy and not accessible to the same level as Shaymin is. Shaymin will be tested in various decks. Remember Lucian? Now it's searchable.
The supporters like Judge are something that can be used to an extent. Dual Balls will be huge due to Uxie/Mesprit/Azelf spamming, but that's pretty much it for the trainer side. We got no stadiums...
So yeah, Onix is playable.