You will Watch The Grim Adventures Of Billy and Mandy Season 4 Episode 12 online for free episodes with HQ / high quality. Stream cartoons The Grim Adventures Of Billy and Mandy Episode 51 The Firebird Sweet: When Billy buys a new cereal, a phoenix emerges from the box and attaches to his head, annoying everybody. Since the phoenix can’t be removed because it revives every time it is destroyed, Billy, Mandy and Grim seek help by going to the factory where the cereal is produced, which is run by Eris, the goddess of chaos. In the end, Mandy tricks the phoenix into leaving Billy and attacking Eris instead. In the end, it is revealed that all the events were really an episode-within-an-episode.