|Bio: The Black Mercy is able to give whoever it's attached to
whatever they desire--in the form of a dream. When Mongul
arrived at the Fortress of Solitude on Superman's birthday, the
Black Mercy did just this to Superman--putting him back on a
very-much alive Krypton, with a wife and son. The dream state is
only ended when the creature is broken free from its host.
Superman's dream ended when the creature was torn off of him by
Batman--not liking this, the Black Mercy attached itself to
Batman, causing him to relive the night of his parents' death.
Despite his father beating up the thug, he was shown the same
gruesome scene he had seen as a child when the creature was
pulled off of him by Wonder Woman.
The Black Mercy eventually ended up on Mongul, where it still
has him in a dream-induced state.