One idea could be a crossover with a post - apocalyptic zombie series. The characters from Left for Dead could find themselves in a different zombie - infested world and have to adapt to new threats and survivors. For example, they might encounter a group that has a very different approach to survival, like a religious cult that believes the zombies are a form of divine punishment. This could lead to conflicts and alliances as the Left for Dead characters try to find their way back to their own world.
Perhaps Percy is left for dead in a magical trap set by an old enemy. As he tries to escape, he befriends a strange creature that he initially thought was an enemy but turns out to be a key to his survival. He has to rely on his wits and newfound friendship to get out and seek revenge on those who left him.
One interesting concept could be a crossover with another post - apocalyptic game, like adding characters from Fallout into the Left 4 Dead universe. They could bring their own unique skills and weapons, which would change the gameplay dynamic. For example, a Fallout character might have a Pip - Boy that could be used to detect special items or infected in a different way.
Well, perhaps the Flood from Halo somehow gets mixed up with the zombie virus in the Walking Dead universe. The characters from both worlds would then have to figure out how to stop this new super - virus. They could form alliances between Spartans and some of the more capable survivors from the Walking Dead. For example, Daryl could team up with a Spartan to take on hordes of Flood - zombies. It would be a really chaotic and action - packed scenario.
One idea could be that the Winchester brothers from Supernatural end up in the world of The Walking Dead. They could use their hunting skills to fight off the walkers. Maybe they'd discover that the zombies are somehow related to a demonic presence and try to find a way to stop it.
One idea could be that the Winchesters find themselves in the world of The Walking Dead. They might use their hunting skills to deal with both the zombies and any supernatural elements that start to emerge in that world. For example, they could discover that a witch is causing the zombie apocalypse as part of a dark spell.
One idea could be that Bella, with her unique ability to attract vampires in her original story, has an unexpected reaction to the zombies in The Walking Dead universe. Maybe her scent or some hidden power she has confuses the zombies, leading to some comical or strategic situations for her group.
Well, perhaps the Cullens could form an alliance with a group of survivors from The Walking Dead. They could use their knowledge of the area around Forks and their skills to help each other. For example, the vampires could protect the humans at night when the walkers are most dangerous, and the humans could help the vampires during the day when they are more vulnerable. And what if Bella's special ability as a shield could be used to protect a whole group from the walkers?
One idea could be that the hunter has been tracking the witch for a long time. But when he finally catches up to her, he realizes she's not as evil as he thought. Instead, she's been trying to protect a group of survivors in her own strange way.
Perhaps Voldemort somehow manages to bring the Left 4 Dead zombies into the wizarding world. The Order of the Phoenix and the Death Eaters are forced to team up to survive. The Death Eaters' dark magic might be used in new and unexpected ways against the zombies, and the Order's more defensive and protective spells would also be crucial. Harry, being the hero, could figure out a way to stop Voldemort from bringing in more zombies and find a way to send the existing ones back.
One idea could be that some of the Sons of Anarchy members find themselves in the world of The Walking Dead. They might use their motorcycle skills to outrun the walkers in the open roads. Maybe they try to form an alliance with Rick's group, bringing their own set of survival skills like fixing vehicles and making weapons from scraps.