I wonder what this means for the games. Will N be reappearing with Zekrom in Black 2 and Reshiram in White 2, to show them as sequels? Wouldn't that be odd if Black Kyurem who is based on Zekrom will appear in the former as well? And of course, White Kyurem in the other. Although maybe the Kyurem formes can actually fly (as unbelievable as it seems to me) and that shadow in the animated promo is one of Kyurem's formes instead. Hmm.
But can't the original Kyurem fly as well? (it learns the Fly HM despite having wonky wings)
Anyway, back on topic: At the start of the trailer with N in it, I've always wondered what that shadow below him was. It didn't look anything like Reshiram or Zekrom, but after seeing the above posts, I got to agree that the shadow does look like one of Kyurem's formes.