The Molten Core card back was a pre-order intensive for the second Hearthstone adventure called Blackrock Mountain. Players had to purchase the entire adventure with real world money or iTunes / Google Play credit before the official April 2015 release date to receive the unique card back.
Blackrock Mountain was the second adventure released by Blizzard Entertainment. The campaign featured 5 wings that could be unlocked individually for $6.99 USD or 700 gold. The entire campaign could also be unlocked at once for $24.99.