Spoiler alert: The band appeared as wildling warriors in last night's episode "Hardhome," in which Lord Commander of the Night's Watch Jon Snow tried to rally some wildlings to prepare for the oncoming battle with the White Walkers, only to have the undead come knock down their walls and decimate nearly everyone in sight, turning them into even more undead warriors. As far as TV sequences go, it doesn't get more metal.
Here's what the band's Brann Dailor (which is a pretty "Thrones"-ish name) had to say about it, as reported by Stereogum:
"It was such an incredible experience to be on set as extras for our collective favorite show Game Of Thrones and to be wildlings murdered and then brought back to life by White Walkers was beyond amazing. I watched my best friends Brent and Bill, murdered right in front of me as I myself was stabbed in the stomach and had my throat slit multiple times, and I didn’t mind at all. It made me love being in Mastodon even more. We are more than privileged and honored to have been a part of one of the greatest stories ever told on film, and the catering wasn’t bad either."
Mastodon previously submitted the song "White Walker" for the Catch the Throne Vol. 2 mixtape earlier this year.