Chernabog is a character who appears in the second half of the fourth season of Once Upon a Time after being released from the Sorcerer Hat. Here, Chernabog is still a demon, but is always referred to as "The Chernabog", and has a satyr-like appearance with its dark aura. It seeks the person with the heart that has the darkest potential, and it is not necessarily a person who had done bad things but simply a person who had the potential to be evil. This can be shown by the Chernabog trying to get Emma and not Regina; the reason being that Emma, being a child of a couple's True Love, can either be a mighty hero or a terrible villain. The Chernabog also went after Maleficent in the past after she along with the other Queens of Darkness and Rumplestiltskin attempted to steal the Dark Curse. It may have been because Maleficent was pregnant at the time, and thus carried a heart with the greatest potential for darkness.
In Storybrooke, the beast was defeated by tricking it over the town line and since the creature was made of pure dark magic, it was completely destroyed after crossing over.
