A mysterious space craft is discovered underground by Project Applecore, a program by Lex Corp. They accidentally unleash the ultimate destructive alien known as Doomsday from within. Doomsday kills all of Applecore's workers and then proceeds to rampage across across Kansas till it reaches the city of Metropolis. Superman races in to stop Doomsday's killing spree in the city but finds the creature an even match. Giving it his all, Superman throws everything he can at the creature till ultimately sacrificing himself in a move that effectively kills both Doomsday, and himself.
Superman's funeral is held as the world mourns. But a week or so later, a hand bursts out of Superman's grave as the man of steel apparently takes to the sky again and resumes hero work. But things are off about him as he seems... different and also seems to completely have forgotten he was in a romantic relationship with Lois Lane.
It is revealed through her investigative reporting work that this Superman is actually a clone of Superman created by Lex Corp who has Superman's body in Lex's company. But then Superman's body vanishes, as the robot at the Fortress of Solitude is able to track him down once it figures out Superman is not actually dead, but in a healing coma, where his heart beats once every 17 days. While Superman struggles at his North Pole hideaway to regain his strength, the Superman clone starts taking things too far with the law and even begins killing off super villains, starting with Toyman.
The government turns on this Dark Superman, not knowing he's a fake, and so the real Superman has to race to the rescue once more but while only partly recovered to battle this false clone through the city.
Quantom X ★
Answer: In the comic book, Doomsday was put in a strait-jacket, strapped in metal bondage and placed in a cube like metal prison buried deep in the earth. It took him centuries just to break the bonds, then spent more centuries just punching his way out. With earthquakes, volcanoes and other natural disasters those events could shift Doomsday's prison to the surface.