RE: Keldeo EX / Blastoise (With and without Black Kyurem EX)
I don't particularly think Virizion's acceleration is very good. I don't know what the format will look like then, so it's impossible to say, but the ability is where I see it shining as a means of stopping HTL, and the acceleration is simply a nice added effect. It's very clunky to rely on; it takes two turns for Virizion to be able to use its attack meaning that you'll only be doing real damage on your third turn; quite late in a format such as the one we have now. Not only that, but the time you send setting up Virizion could have been spent setting up a different attacker. To really make effective use of Virizion, you would have to use the attack multiple times in a row and fill your field with energy, but that's really slow and Virizion may get knocked out before that happens.
Against Keldeo/Blastoise, if the deck still works, Virizion isn't going to be the card that ruins it. Genesect EX is a much better "counter" to Keldeo/Blastoise, but even then, Keldeo has BKEX to get rid of the Genesect very quickly. I don't think there will ever be a direct counter to this deck as Blastoise always has something to get around it, whether it be an extremely high damage output or the use of Tropical Beach to handle Frozen City.