One of the biggest storylines that Game of Thrones hasn't yet fully explained is Bran Stark’s purpose as the Three-Eyed Raven. We know he wargs into humans and animals alike, and has the greensight ability which allows him to see past and present events without actually being there. Before truly taking hold of these powers upon the death of the previous Three-Eyed Raven, most of what Bran saw came to him in random visions. And one of those visions from season 4 might actually be very important in the series's final two episodes.
One fan on Reddit, user JasonDeBaxter1997, points out that in the season 4 episode “The Lion and the Rose,” Bran has a vision of a dragon’s shadow flying over King’s Landing. "It actually appeared to be from the Dragons' perspective flying over the buildings looking at it's [sic] own shadow," the Redditor wrote. "Could this be a vision of the future where Bran wargs into a dragon during Ep 5 battle?" (To us, it looks like the perspective isn't a dragon looking at its own shadow, but of something else looking at the dragon's shadow. Perhaps ... another dragon?)
The user then points to the final season’s episode 5 teaser, which shows Euron Greyjoy looking surprised at something above him in the sky—a moment fans have been speculating about since the preview’s release. Acknowledging that it could be Drogon wearing armor or even more dragons we didn’t know existed, the Redditor also thinks it could be Rhaegal, resurrected by Bran. As the Redditor points out, the previous Three-Eyed Raven told Bran that he would never walk again, "but you will fly."
While we don’t have evidence to prove a warg can resurrect a dead human or animal (though wargs close to dying have entered the bodies of the animals they occasionally control, and lived on there after their human body has died), Redditor Scottyp2608 pointed out in the comments section that dragons are made with old Valyrian magic, making it difficult to say the same rules have to apply to them.
Fans have been speculating for years what that King’s Landing vision was foreshadowing. But given the fact that part of Bran's vision—the Throne room destroyed and covered in what looks like snow or ash—also appeared in Dany's vision at the House of the Undying in season 2, it seems clear that at least some of that vision will come to pass.