Pokemon is really going big with these new releases for Hoopa and... Whatever this is. Probably not a new Pokemon, but a form of something. The hands almost remind me of Zekrom, with the overlaying claws.
Looks like a Megazord from Power Rangers. (Actually, Hoopa does too, but oh well.)
Also, the three glowing spots. I know WPM said two, but I think the light behind the words, given that there is a similar spot on his other hand and that seems to be where his other hand would be, means he has a third spot there. Could be representing something? Zygarde, Xerneas, and Yveltal? They all glow, don't they? Can't remember if the bird does.
But I'm going to be the big speculator and hope that this is somehow related to the original dragon. I mentioned the hand resemblance to Zekrom already, and maybe the glowing spots represent the three stones connected to Kyurem, Reshiram, and Zekrom?
One can dream.
It's worth noting that what appears to be four large spikes separated into sets of two (on its head) are actually many smaller spikes that look very similar in shape to those of Zygarde. As poor as my highlighting effort in paint is, you can actually see the small spikes side-by-side if you zoom in on the part of the image where lightning illuminates the silhouette. They seem to be behind a vaguely diamond-shaped head, so they could also be protruding from the back of its neck, where the skull meets the protruding neck element. It also seems to lack a clear division below its waist (which would indicate the presence of legs), so it could either have a serpentine or root-like lower half, the former linking it to Zygarde, or the latter possibly implying Xerneas' involvement in the transformation
