[GoT Finale Spoiler] How did the Wall Fall?

We should be used to tragic Game of Thrones deaths by now, but the one in episode 6 of season 7 was a true gut-puncher: RIP Viserion. And welcome to this crazy world, zombie Viserion. From a purely story-telling perspective, his transformation to a wight makes the plot even more intriguing: there are now dragons…