The Black Mercy
Name given to a plant-like alien parasitic entity that functions similarly to a fungus. The non-sentient creature appears as a collection of reddish discs with a number of brown, sinewy tentacles that radiate outward from its center. The Black Mercy attaches itself to a victim's chest while wrapping its tendrils around the torso, and subsists by feeding on its prey's bio-aura. The entity keeps its victim docile by placing him/her in a trance-like state while filling the host's mind with visions of his/her strongest desires being fulfilled. The entity must be handled with specialized gauntlets that negate its powerful influence, as it can affect even the most invulnerable of potential hosts. Apparently, the only means of escape is through subconscious resistance of the delusion, corrupting it into something causing traumatic emotional distress to allow the victim to shake off the parasite.
Mongul employs Black Mercy as an instrument of revenge against Superman by disguising it as an anonymous birthday gift, but the Man of Steel is freed from the creature's clutches by the combined efforts of Batman, the second Robin and Wonder Woman. In the end, Mongul himself falls victim to the creature's influence when Robin affixes it to the alien tyrant's chest (SA No. 11, 1985: "For The Man Who Has Everything").