New Amalgam Universe by Red-Rum-18: Justice Avengers/Enemies/Secret Society of Evil 1
You are all probably wondering how the New Amalgam Universe came to be, eh? Well, gather ye 'round and I'll spin you the yarn of:
The Anti-Monitor, sore from his defeat at the hands of his multiverse's heroes in the "Crisis on Infinite Earths", decided to enlist the help of a super-being from another multiverse. For eons, the immortal eraser of worlds scoured every era of time in every universe he can reach for the one he can call his equal, with the same goal at heart: Destruction for Destruction's Sake. And at last, the Anti-Monitor joined forces with his true counterpart: Aron the Rogue Watcher. Aron had long suffered the responsibility of watching the lesser beings of his universe slaughter each other without interfering, so he decided to take matters into his own hands, trying repeatedly to destroy and rebuild his universe in his own image, without pain and suffering.
With their combined powers, Aron and the Anti-Monitor slowly but surely merged their universes together, the most similar characters from each interacting with each other and the most similar events transpiring at the same time.
The most significant event to bring the heroes and villains of each universe together is the arrival of both Galactus and Imperiex to the same Earth. Galactus, from Aron's universe, wished to consume Earth for sustenance and to rebirth the universe, while Imperiex, epitome of entropy and decay, wanted to destroy Earth to reignite the Big Bang.
Galactus and his heralds (Terrax, Firelord, and Morg) squared off against Imperiex and his I-Probes over the whole of New York City, which was cosmically merging with Metropolis from the other universe.
While the Avengers, X-Men, Guardians of the Galaxy, Justice League, Teen Titans, and Green Lantern Corps tried to stop the war, which was slowly tearing both universes apart, the most brilliant minds from both Earths gathered in the Sanctum of Fate (Sanctum Sanctorum + Tower of Fate), a fused-together magical fortress now maintained by the Sorcerers Supreme of both universes, Dr. Strange and Dr. Fate. The council came to the conclusion that the is only one being capable of matching the power of Galactus and Imperiex: Onslaught!
Professor Xavier and his archenemy Magneto both agreed to the magical process, conducted by Strange and Fate, to reconstruct Onslaught from Xavier's and Magneto's psyches.
The reborn Onslaught was supposed to be magically programmed to serve Strange and Fate, but something went amiss: As Onslaught was slowly remoleded, Iron Man's armor involuntarily launched a missile at its form, and Brainiac, a 12th level intelligent AI from Anti-Monitor's world, exited the missile and took over Onslaught's mind. "Brainislaught" attacked Galactus and Imperiex, so he can reclaim the Earth, absorb its data, and destroy it.
As the war between Galactus, Imperiex, and Brainisalught raged on, they used their powers to compel their Earths' villains, from Lex Luthor and the Red Skull to Darkseid and Thanos, to attack the heroes trying to interfere.
In the end, the battles took their toll and the two universes imploded, destroying everything; not even Aron and the Anti-Monitor were safe from their own meddling.
The only two beings left were the Gods known as the One-Above-All and the Presence, both of whom were only at half-strength. They both decided to merge their powers and forms together in order to restore existence. They amalgamated and became "The Presence-Above-All."
The Presence-Above-All's first creation was "Dr. Strangefate" (Dr. Strange + Dr. Fate), the only being in the universe who knows the truth behind its existence.
And well... you know the rest.