Adventure Time: Explore the Dungeon Because I Don't Know came out on the 15th in EU and is being released tomorrow in North America. According to Pendleton Ward, the game has a "big reveal" that will later come up in the show. And now, thanks to the Power of the Interwebs! Here it is! Skip to 13:16 for the end of the boss battle.
It even includes a little Bubbline! Insert obligatory Bubbline picture.