Satan (This Is The End)

"Oh, you've got to be fucking shitting me!"

- Jay Baruchel This version of Satan was the final and true main antagonist of the comedy-horror film, This Is The End. Satan is dead-set on bringing forth Armageddon onto the Earth and destroying all life. This is presumably so he can increase his amount doomed souls forced to do his bidding. He unleashed his demons both to possess humans to make them do his evil bidding (like the one whom rape and possessed Jonah Hill) and wreak havoc and kill anyone whom still alive during the apocalypse.

Appearance
Satan's appearance is depicted in a drawing in James Franco's Bible, as a gigantic, hoofed-legged, horned demon with several eel-like heads protruding from his back.

When Jay and Seth confront Satan at the climax, he indeed resembles the drawing, but is colossal in size and also made of hardened lava and has a large, exposed penis.

Unleashed
During the apocalypse, Satan was released from hell alongside other demons where they quickly either corrupt or slaughtered humans that they encountered. While not physically seen, his image was shown in Franco's Bible as Jay explained to them that apocalypse was occured all over the world.

Encountering Jay and Seth
Though was referenced by Jay and his presence can be felt over the course of the film, Satan himself was not seen until Seth Rogen and Jay Baruchel confront him. However, their reconciliation and admission of their past wrongdoings is what saved them from eternal damnation and they were Raptured into Heaven. At first, because Jay was the first one whom truly redeemed himself, he was the one whom being raptured by a holy beam that pulled him to Heaven. Jay tries to take Seth with him, but suddenly, Satan tries to attack them with one of his tentacles only for the beam deflect it. Just then, beam that taking Jay was slowed down due to him carrying Seth whom yet to fully admissioned their wrongdoing. Realized his past mistakes on Jay, Seth let himself fall into Satan's mouth much to Jay's agony. But suddenly, another holy beam raptures Seth at the last seconds much to Jay's joy, where the beam nearly sliced Satan into 2 where the worst injuries was on his penis that sliced off by the beam. Satan survived with the severe wounds as he helplessly watch Seth and Jay carried to heaven, with his severed penis in his hands. It can be assumed that Satan was still alive and still continue the rampage.

Trivia

 * According to Nightmare Fuel section of TV Tropes of the movie, Satan's size was so huge that his penis was as large as split-level house.