Mastodon recently participated in a Game of Thrones mixtape, entitled 'Catch The Throne: The Mixtape Vol 2'. They introduced the song "White Walker".
After the release they had the opportunity to step in and make an appearance on an episode of Game of Thrones. The episode was "Hardhome" which aired on May 31, 2015. Drummer and vocalist Brann Dailor had this to say about the experience.
It was such an incredible experience to be on set as extras for our collective favourite 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 honoured to have been a part of one of the greatest stories ever told on film - and the catering wasn't bad either.