[[WMG: The Doomsday World is a fusion of all worlds that have ended or are about to.]] The End of the World isn't just a time, it's a place. The Valley of Megiddo. The part of the multiverse that's circling the drain. Thus, any world that ends fuses with it, with the ZombieApocalypse waiting for them. This is why Bok Zombies can respawn, defeat one, and eventually a timeline where it wasn't killed manifests. This also means that worlds that are in critical danger of ending have a very thin dimensional wall, hence the worlds of ''VideoGame/MegaManBattleNetwork'' and ''[[WMG/MetalGear Metal Gear]]'' have had incursions.
* [[WMG/MetalGear This also explains Vamp.]]

* For a brief period of time, [[Main/{{TheHeartless}} The Heartless]] of Xehanort from ''[[WMG/{{KingdomHearts}} Kingdom Hearts]]'' made his base here. "The End of the World" after all.
* Also, the entirety of ''VideoGame/HellgateLondon'' takes place there with the human "survivors" still battling the demonic and undead hordes out of a mistaken belief that their world still exists and can be saved.
* The abyss from FromTheAbyss is either the Doomsday World itself, or a tunnel leading to the Doomsday World.

[[WMG: Dark Matter is a form of Main/{{Nanomachines}}]]
Oh, there's a lot of psychic/spiritual energy involved, but ultimately the Immortals are just the remnants of Main/NeglectfulPrecursors who believe their own mythology. It's latched onto Dark Energy as its power source, which is why Sunlight can destroy it.
* As ''VideoGame/MetalGearSolid4'' shows us, nanotech can do a ''lot''.
[[WMG: The world of Boktai is the [[Main/{{AfterTheEnd}} aftermath of the apocalypse]] in the Mega Man Universe]]
This would explain the SchizoTech. An advanced solar-powered gun, connections to Battle Network's net, a bank with computer terminals, and a huge and apparently quite complex clocktower all exist in an apparently medieval setting?
[[WMG: Galaxy Universe/The Will of the Galaxy was formed from remnants of [[Franchise/SailorMoon Sailor Galaxia]]'s Chaos-afflicted energies.]]
* Her compassion was twisted by the energies of Chaos: in an attempt to free the Universe from Death, it became Klorofolun, which causes Undeath.

[[WMG: The vampires in Lunar Knights are a degenerates]]
And immortals are still the same.

after Ratosk was slain the stock of immortals suffered as a result. Next line of vampires was weaker as a result, lacking the fabulous powers of their progenitors. In order to even hold a candle to them, the vampires had to not only infuse themselves with the power of the earth itself (the terrenials) but also build advanced armours and machines to back them up. the immortals decided that they could afford to let the vampires run amok on earth in their stead as their reliance on their supernatural and technological crutches would make them easy to overthrow if they became a problem. Hell even two kids with a sword and gun between them absolutely wrecked the vampires in a matter of days.