Revealing mistake: An electronics shop has TVs on display, all showing a newscast about rising crime rates in Metropolis since Superman's death, and the window is broken by a brick as some thugs start stealing the TVs. Watch closely as they pull them out, the TVs have no power cords, but are on. Most noticeably on the second one when the guy has the TV lifted up, no cord seen, and yet the image still displays on the TV until he pulls it out of the window. (00:33:05)
Continuity mistake: Towards the beginning of the film, you see Clark pick up and then set down a picture of his mother down by his computer towers. Then 30 minutes into the film you see Lois look across over at that same picture after Superman's death and the computer towers change in design. (00:04:30 - 00:30:45)
Continuity mistake: After the scene in the Daily Planet where Lois and Perry are talking about Clark missing and that Lois should go see friends or family, it cuts to her driving down a road by large corn fields going to Martha Kent's house. She is driving with her right hand on the top of the steering wheel and her left arm hanging out the window, but with her hand and wrist propped up on the seal. It then cuts to a different angle as the car is driving by and suddenly her left arm looks extremely weird in some animation error. It appears it is just the elbow of her arm out the window, but that it has somehow merged with the door and she has become part of the car. Also her right hand is no longer at the top of her steering wheel and her head rest on her seat is suddenly not extended up as much. (00:30:55)
Continuity mistake: After Superman's funeral, Lois is sitting in her cubicle at the Daily Planet reading a newspaper. When Perry White walks up and talks about there not being word from Clark Kent, it cuts to a shot from further back. Some of the papers on the wall behind her vanish, the pencil on her desk vanishes, the papers pinned to her bulletin board to her right change shape slightly, especially the one towards the center bottom becomes straighter instead of crooked and longer, also displaying different text. And the distance between the edge of her bulletin board and the other cubicle wall increases. (00:30:15)
Continuity mistake: At the start of the scene showing Superman's funeral, there is a yellow guard rail around the memorial stand with his coffin in front of the podium. Standing in front of the yellow rail are 13 police officers in full uniform, 7 on one side and 6 on the other. The shot cuts to the audience for a moment, and then shows the podium and memorial again from a distance shot, and suddenly all the police standing by the coffin have vanished. (00:28:10)
Continuity mistake: As Superman is emerging from the smoke after the impact, the amount of damage to his suit on his right shoulder changes between shots of him, the close up of Lois and the back to him. The damage on the chest area also changes from appearing near perfect to very jagged. And the blood dripping down from his mouth also becomes thinner. (00:26:50)
Continuity mistake: Superman grabs Doomsday and rockets upwards with him to save a little girl and to take the creature into space. When he first starts going up, Doomsday's arms are forced down at his sides, but slightly in front of him from the force. But when the shot cuts to a distance shot, suddenly Doomsday's arms are stretched up in the air like how Superman normal flies. (00:25:25)
Continuity mistake: Lois is reading a newspaper in her cubicle about the death of Superman, and there is a pencil on her desk on top of some papers. A few shots later when Perry White gets closer to her to tell her that Kent is probably fine, the pencil turns around facing a different direction, and the papers it is on move also. A stapler also suddenly appears next to her computer, and the brown book on the far end of her desk moves closer to her and turns around so the spine is facing the wall to Lois right and the pages facing her computer when it was the spine facing her computer first. (00:30:35)
Revealing mistake: Doomsday drops Superman once he hears a little girl crying and walks up to her to try and smash her. As he is walking up, it shows a close up of the crying girl and she is wearing a pink shirt with denim overalls on. But look closely and you can see a mistake in how she was drawn. The straps of the overalls are incomplete and stop a few centimeters away from the buttons on them that are supposed to hold the straps in place, and the buttons are between the straps and her overalls, with a gap between the buttons and the front part as well. It's not connected at all and should be falling off her. (00:25:15)
Continuity mistake: After Lois and Jimmy settle down by some rubble to watch the fight more, Doomsday is shown picking Superman up by his head before he begins punching his gut. In that shot, Doomsday's right arm is straight down by his side, and also the bone spikes have vanished off his knuckles. It then cuts to a close up and suddenly Doomsday's arm is drawn back some behind his back, and his knuckle spikes reappear. (00:24:45)
Continuity mistake: After Superman is flung out of the subway and hits a building, then lands on the ground face down, Doomsday leaps out of the hole and you can see what appears to be a brown 80's SUV, or a truck with a camper, behind him next to some civilians. The camera angle changes a side shot of him as Doomsday turns his attention to the civilians and charges them, and now the SUV has vanished. (00:23:40)
Continuity mistake: When Superman is launched out of the ground from his fight in the subway with Doomsday, he smashes into a brown building with yellow windows. The windows on the left side of the building are in a tall vertical column, with several horizontal rows of yellow windows on the rest of the building. When Superman hits the building, you can see he hits between the area of two horizontal rows of yellow windows. But it cuts to a close up and suddenly he is lined up with one of the rows. (00:23:35)
Continuity mistake: Doomsday picks Superman up by the head and is about to start pounding him in the gut when Lois and Jimmy run up to some rubble behind the creature and duck down. Jimmy then raises up his camera to his face to snap a picture, but when it changes to a shot from behind Jimmy and Lois, suddenly his camera is back down. (00:24:40)
Continuity mistake: After Jimmy takes a picture of the hole in the ground above the subway station, the shot pulls back and shows the hole, with several people gathered around it and some cars. Then suddenly some of the road is pushed up from Doomsday and Superman fighting below and the people turn to look. The angle then changes before more road is pushed up on the other side of the hole, and suddenly the part of the road that was pushed up in the previous shot is back down to normal, the green cars have vanished and a white one appears next to this new pushed up spot, and a guy wearing a white shirt suddenly appears where the road is pushed up. Also the crosswalk lines once again vanish. (00:23:35)
Continuity mistake: When Doomsday backhand slaps Superman down the tunnel, Superman skids along the roof for a moment first, and leaves a good amount of damage to it in the process before he falls to the rails below. But then when the subway train is coming and Doomsday turns his attention to it, the damage Superman made to the roof of tunnel has completely fixed itself. Also some of the lines at the start of the tunnel dividing the different concrete slabs have vanished. (00:23:10)
Continuity mistake: Once Doomsday slams Superman down through the ground into a subway station, he has him by the neck against the floor, and then clasps his other hand around Superman's neck. When he does, Superman looks up at him with his eyes just before he blasts Doomsday away with his laser vision. But his head is still turned sideways. It cuts to a different angle and suddenly Superman's head is fully facing up towards Doomsday. Also the grip in how Superman and Doomsday are holding each other changes a bit, notably with their hands. (00:22:45)
Continuity mistake: Doomsday leaps into the air and smashes Superman down into the ground, crashing down into a subway station. As they are hitting the floor, you can see the brown columns holding up the roof are almost to the edge of the walkway by the tracks and touches where the tan area of the floor changes to a light green color at the end. But then Superman shoots Doomsday back with his laser vision and Doomsday looks at him angrily, and now the columns have a good few feet between them and the edge of the walk way. (00:22:40)
Continuity mistake: Doomsday and Superman leave a sizable hole in the roof of the subway station as they slam in through the streets above. But when Superman throws Doomsday down onto the tracks, the shot shows the same spot where they made the hole coming in, only now the roof is devoid of any damage and the hole entirely gone. (00:22:55)
Continuity mistake: Once Superman throws Doomsday down onto the subway tracks, he flies at him and Doomsday back hand slaps him hard down the tunnel. Superman lands on his face on the rails, and you can see the sleepers on the ground under the rails. When the camera changes angles as Doomsday approaches him, the sleepers suddenly become much larger. (00:23:05)
Continuity mistake: Just before Doomsday ploughs through the fence of the power station carrying Superman with him, you see down the street he is about to go on that there is a yellow 18 wheeler with gray trailer and an pinkish car on the left side of the street. But then it cuts to a close up of those same vehicles as Doomsday steps on one to jump, and suddenly both have turned into green cars. (00:22:35)
Chosen answer: When they call Doomsday a machine, they don't mean a literal machine. Just that he was built/designed. The comics were much the same. Doomsday was created by placing a baby on the most dangerous planet in the universe, and cloning that baby every time it died, forcing it to adapt. Doomsday eventually escaped this torture.
MasterOfAll