Final Crisis/WMG

Final Crisis is the prequel to The Great Darkness Saga.
This is the crushing defeat that ended with Darkseid's death, leading to his eventual resurrection in the distant future. Confirmed!

Final Crisis Never Happened''.
The idea of the event exists, but the story itself went into the Limbo that itself told about in Superman: Beyond. The actual events never happened in universe. The Kicker, the effects made by the event, IE, Batman "Dying," The Flash returning, and the other characters who have been changed in someway, still carry on. Like a certain other event.....
 * That might explain how easy the cleanup apparently was.
 * Confirmed by JLA's Rock of Ages arc from ten years earlier. It's stated that every time Darkseid attempts something big with the universe it causes a reboot where nothing really happened. Superman's use of the Miracle Machine and the Rock of Ages from Metron's chair at the end of FC circumvents Darkseid's resurrection.

Not only is Mandrakk the original Monitor from the first Crisis On Infinite Earths, he's violently insane due to the creation of the other Monitors
Its heavily implied and oft-theorized that Mandrakk was the original Monitor. What changed for him that could have driven him so mad and violent? Mr. Mind's Munchies. When the 52 new universes were created, 52 new monitors were also created- but from where? From Mandrakk. 52 pieces of his essence/mind/soul were torn out and expanded into separate corporeal beings, each with their own retroactive history like the world they represent. Mandrakk was driven mad by the loss of so many pieces, due either to essence loss leaving not enough mind to be sane, unimaginable pain, incredible weakness of being stretched thin leading to maddening hunger, or the multiverse's worst ever recorded case of postpartum depression.
 * This makes a hell of a lot of sense. Poor guy.

Darkseid lost because he found an incorrect Anti-Life Equation
The correct one, of course, involves Squirrel Girl, also known as The Anti-Life.