It's kind of like Kyurem EX, except better. Dragon Fang has 60 and a chance of paralysis for {L}{C}{C}, which is a mediocre attack. Things get more interesting with Freeze Bolt, which does 150 for {W}{L}{L}{C}, with the cost of not being able to use it next turn. Then you get its ACE SPEC Crystal Wall, which boosts its HP up to 300. I can see it being used in a tank deck, with healing cards like Potion to keep it alive as long as possible to do maximum damage. It will have to be played with cards like Sableye DEX or Recycle EPO to get your Crystal Wall back from the discard when Black Kyurem is Knocked Out. You'll probably have a hard time against Garchomp/ Altaria because it can take Black Kyurem out in one shot provided it has 3 Altarias in play. You'll need to do some serious Altaria killing in order to beat the deck. You could play it with Eels. Retreat each turn and Dynamotor the 3 Electric Energies back on to the one you retreated and send up a previously powered up Black Kyurem. Overall, I'd give it a 7/10 for playability.
Edit: You can also play it with Altaria and Darkrai EX to OHKO everything in the format turn after turn, as long as you have 2 Black Kyurems charged.