Game Of Thrones Theory: Bran Wargs Into Night King's Dragon In Season 8
6. Bran's An Extremely Powerful Warg
Bran's power has grown exponentially over the course of the series. While even early on we saw him have dreams that hinted at something inside of him, it wasn't until Season 3 we got a real taste of his abilities.
There, he was able to not only warg into his direwolf, Summer, but also Hodor. To warg into a beast is par for the course, but a human is a whole other matter, and that was only half of the connection between Bran and Hodor that further revealed just how powerful he truly was, creating a time loop whereby his actions in the present informed the past.
Of course, he's not just a warg, he's also a greenseer, meaning he has visions of things to come, a skill he has honed under the tutelage of the Three-Eyed Raven - i.e. the most powerful greenseer in existence - until the point he actually becomes the Three-Eyed Raven. Ergo, Bran is the most powerful greenseer alive, which also makes him the most powerful warg alive. He can see the whole past. He can glimpse the future. He can warg into a living person, so what's to say he can't warg into an undead dragon?