In the current Justice League Dark run, writer James Tynion IV and artist Álvaro Martínez created one of DC's most sinister new villains in recent memory with the Upside-Down Man. The book shaped him as a menace to all of magic in the universe and linked the horrific entity to very creation of magic itself.
In The Witching Hour event, Upside-Down Man fully cut loose in a story that redefined a lot of what we understood thought magic to be. In the process, the door is open for the Upside-Down Man to become an even greater threat to the supernatural side of the DCU.
WHO IS THE UPSIDE-DOWN MAN?
The Upside-Down Man was formed when creation gave birth to light and dark energy, which both became the two sides of magic. The light formed Hecate, who in turn sealed away the darkness. The latter's avatar was this disfigured creature known as the Upside-Down Man, as he was literally the inverse of the good that magic could be used for.
Trapped in his dark dimension, he had warped monsters called the Otherkind working for him. Using these creatures, he tried to break the barrier Hecate formed, trying to come over to Earth to reclaim the magic his 'sister' blessed mankind with. This magic gave rise to the Lords of Order and the pantheons of gods around the world, but the Upside-Down Man felt this was his power that was stolen and disbursed without permission. He's connected to magic, since its part of his very essence, and he wanted to reclaim it, using the Otherkind as his servants.
WHAT CAN THE VILLAIN DO?
The Upside-Down Man usually operates using the Otherkind as foot-soldiers who can infiltrate the planet, while warping dead bodies and monsters along the way for their own nefarious schemes. His power is so immense that he infected the Parliament of Trees and in a brutal battle, he turned Detective Chimp into liquid and even transformed Swamp Thing to ash.
He also killed Constantine and instigated the wave of dark energy that destroyed Nanda Parbat, making it clear that he was all about revenge. The Upside-Down Man's strength stood in making magic backfire on wielders he felt unworthy, and his other powers include transmutating enemies, regeneration, flight, manipulating energy and also affecting the blood of people. He's more or less a dark god and Wonder Woman's worst nightmare, since she was blessed with Hecate's mark to fight him and the Otherkind. But as she found out, this being really was a primitive creature that was near omnipotent as he was tethered to creation.
HOW WAS HE DEFEATED?
When Hecate's mark manifested on Diana, she was able to seal the rift and lock him away temporarily. However, Hecate was simply using Diana to reclaim magic herself, since she hated how mankind corrupted it and stopped worshiping her after she gave it to them. Diana became Hecate's weapon of destruction, but luckily, she saw the light and snapped out of it, realizing that magic had to serve a higher purpose.
Finally understanding what this mystical mark was meant for, Diana wanted to bring the magical world back to a state of balance. Realizing that the Upside-Down Man wouldn't stop coming for revenge, she had Zatanna use her unique set of powers which unlocked the rift. The Upside-Down Man came over for one last meal, grabbing Hecate and feeding on her, before Diana locked them both in the dark realm once more. Wonder Woman sealed the rift once more, hoping the grotesque creature would be sated and feeling as if Hecate got what was coming to her. To her, they deserved each other and with Hecate to devour, it appears the Upside-Down Man got the retribution he sought for eons against the person who exiled him from reality.