Apocalypse World is an alternate universe, one in which the forces of Heaven and Hell are fighting in an eternal battle with humanity caught in the middle. It is connected to the normal world by a portal opened by the Nephilim son of Lucifer -- Jack.
With the Apocalypse having happened, the Earth has been transformed into a barren wasteland littered with the bodies of angels, demons, and humans. Large angel blade-like spikes can be seen protruding from the ground with bodies impaled on them, while the skies crackle with red lightning. Time appears to move differently, as when Castiel first steps through to the rift during the day, he finds himself on the apocalyptic landscape at night. At some point during the various wars that have gone on, the number of humans appears to have dwindled significantly, with the female population taking the more drastic hit.
Demons appear to have a physical form on the earthly plane and no longer require vessels, as evidenced when Castiel is attacked by a horned tempter demon. Angels seem to be much more fierce and brutal warriors, as Bobby Singer told Sam and Dean that the only reason he didn't kill Castiel on sight was because "he wasn't wearing a necklace made out of baby ears." Angels still appear to require vessels, and are more militaristic.
Characters in Apocalypse World
- Bobby Singer - Still a hunter in the post-Apocalyptic wasteland. This Bobby Singer has a self-described "passion" for hunting angels, for which he uses bullets forged from discarded angel blades, with his trusty machine gun, "Rufus."
- Mary Campbell - Killed ten years prior to the present by Azazel. She was a hunter that ran with Bobby Singer, was known to tell the same story about the man she loved, John Winchester, with enough pints of moonshine in her.
- John Winchester - Has been dead for over 40 years, possibly due to Mary refusing to make the deal with Azazel to resurrect him in 1973, causing Sam and Dean to never be born.
- Azazel - After Azazel killed John, Mary refused to make the deal to bring him back. Bobby would go on to tell Sam and Dean that Azazel killed Mary ten years prior, implying that Azazel is still alive in Apocalypse World.
- Michael - Defeated his world's Lucifer, claiming to have ripped him apart over Abilene, Texas. Michael has become a conqueror, bringing death and destruction to the planet rather than paradise.
After Jack inadvertently causes a rift in space and time, Castiel crosses over to investigate. Once through he finds himself on a dark and barren landscape, and is soon attacked by a tempter demon, which is shot and killed by that universe's Bobby Singer.
When Sam and Dean learn about the rift they too, cross over with Castiel, where they meet with Bobby. Castiel and Bobby explain what happened in that universe -- Sam and Dean were never born on that world and thus never saved it from the Apocalypse. Soon after leaving, Sam, Dean, Castiel, and Crowley formulate a plan to trap Lucifer on the other side.
When Lucifer finally locates Kelly Kline's location, Sam and Dean lure him into the Apocalypse World, where Crowley has set up the ingredients for a ritual to close the rift, telling Sam he is missing only the final element: a sacrifice. As Dean attempts to keep Lucifer distracted by riddling him with angel blade bullets from Bobby's machine gun, Crowley intervenes before Lucifer can kill Dean. Lucifer tells Crowley that no matter what he tries, he will lose. Crowley turns to Sam and Dean and bids them a final "Bye, boys" before stabbing himself with an angel blade and completing the ritual. As the rift begins shrinking, Castiel comes marching through it, and with an angel blade in hand drives it into Lucifer as Sam and Dean make their escape. Castiel soon follows, but is almost immediately killed by Lucifer after stepping through. Lucifer then turns his attention to Sam and Dean. However, Mary arrives and begins beating him back with Enochian brass knuckles, until he falls backward into the rift, dragging Mary along with him. On the other side, Lucifer looks on in anger as the rift closes, trapping him along with Mary.
Soon after being stranded, Mary attempts to flee from Lucifer, but doesn't make it far before he captures her. She asks if he is going to kill her, but Lucifer tells her he needs her.
As Lucifer and Mary trek the desolate landscape, Mary stops telling Lucifer it doesn't matter because he will just kill her anyway. Lucifer, goes on to tell her that he needs her as a bargaining chip to get his son back from Sam and Dean. A fireball soon comes barreling towards them, crashing into the earth. In the chaos of the impact, Mary is able to slip away from Lucifer. On the run, she comes across a hunter, who realizes she isn't an angel and tests if she is a demon. When he begins invading Mary's space, she fights back and in the ensuing scuffle, the hunter is impaled by Lucifer punching a hole through his chest.
As they continue on their journey, they are soon met by a flight militaristic of angels, who "sense a creation that sinks of Hell" and demands Lucifer identify himself. When the commanding angel doesn't believe him, telling him Lucifer was killed by the archangel Michael. The angels prepare to smite Lucifer on their leader's command, as their eyes glow blue, Lucifer simply snaps his fingers and disintegrates the lot. This act garners the attention of Michael, who crashes to the earth like a comet, emerging from the crater wings spread open. Realizing the angel before him is indeed Lucifer, he questions him how he is alive, Lucifer casually mentions alternate universes. Lucifer mocks Michael telling him he is a cheap knockoff of his brother, Michael then tells Lucifer of how he ripped his brother apart over Abilene, Texas. Realizing a fight is going to happen, Lucifer sucker punches Michael, but is quickly subdued and captured by Michael.