Marvel is teasing something big for tomorrow, but as you can see from the posts below, they're keeping their cards very close to their chests on this one.
There's speculation that it might be the first trailer for Thor: Ragnarok, but there would usually be more concrete confirmation if it was movie-related, and the Tweet is more likely to have come from the Marvel Studios account if that was the case. The other most popular theory seems to be the announcement of a partnership with Japanese video game developer Square Enix, which has been rumored for a while.
Whatever it is, we'll all know by around this time tomorrow. In the meantime, be sure to share your theories and guess in the usual place.