Continuity mistake: After Superman fails his experiment to cure cancer, Lois walks up wearing just a towel and holding a smaller towel, drying off from a warm bath. It cuts to a different angle and suddenly the parts of her hair draped over the front of her shoulders down her chest are shorter, and the ends of the hair go from a single point to being forked. Her grip on the smaller towel also changes, her hands closer together, and her mouth is suddenly open when the shot changes. (00:08:10)
Continuity mistake: After Tess walks in, Lex turns and begins pressing buttons on a small hand held device. There are three green lights at the top. When the angle changes, suddenly the lights are smaller and his grip on the device changes. (00:06:45)
Continuity mistake: When the laser drill at Project Applecore is first shown, it has open wheels. But once the workers discover Doomsday's ship, the laser drill is seen backing up, and suddenly it has fenders. (00:05:25 - 00:06:20)
Continuity mistake: In Project AppleCore, once the forklift goes by carrying a load, you see in the distance where Dr.Murphy is standing still looking at a wall. It cuts to a close up and suddenly she is walking from the same spot she was standing. (00:05:30)
Continuity mistake: After the workers at Project Applecore discover Doomsday's ship, the scene changes to Lex in his office staring out the window. It cuts to a further shot as Tess walks, and suddenly Lex has moved over some to the left closer to the edge of the window pane. (00:06:30)
Other mistake: After Clark sets down the picture of his mother, Martha, he clicks a button on his keyboard and the monitor for his computer shuts off. Only thing is the button he pressed is the one directly to the left of the Space Bar, which is the Alt button. I don't know of any computer where you press the Alt button, even in a shut down process, to shut the computer down or even just shut off the screen. (00:04:30)
Continuity mistake: Behind Clark when Perry asks him about his flight, the elevator door is seen behind him with its green design lines all over it. Then after talking to Lois, he gets in the elevator and the door closes, and now the diagonal green lines towards the top have become much thinner. (00:04:00 - 00:04:50)
Continuity mistake: At the Daily Planet, Clark picks up a picture of his mother and smiles at it before setting it back down. Between shots, the picture changes slightly, Martha's image becoming larger compared to her background. Most noticeably the window in the barn is closer to her head as well as the bush by her neck. (00:04:30)
Continuity mistake: When Lois and Perry are arguing in his office in the beginning, you can see his many plaques on his wall. Moments later when Perry is standing in his office door way talking to Clark, you can see the same wall and corner behind him. Now there are fewer plaques and they have moved around, most noticeably the round orange one now on the other side of the corner. Also the desk with books on it under the round orange plaque vanishes. (00:03:30 - 00:04:05)
Continuity mistake: Perry asks Clark if he should be packing for his flight and you can see the cubicle directly to Clark's right there are some brown papers of some sort on the wall of the cubicle. Then a moment later in a close up of Clark, the brown items have become a wall calendar. (00:04:05)
Continuity mistake: When Clark goes to pick up the blue lunch box next to his mom's picture, it shows his computer tower at his cubicle. On it above the red light, are two rows of 4 rectangles. Then it changes angles and now the first row of rectangles is thinner and more square shaped. Also between shots the extended gray space between the darker space where the rectangles are and the red light becomes thicker. (00:04:20)
Continuity mistake: After Dark Superman knocks Superman into his memorial stone, Dark Superman (the one dressed in blue) comes down and hovers over Superman (dressed in black) and gloats. Behind him is the bulldozer. After Lois shoots Dark Superman with a Kryptonite beam and then Superman tackles him, they slide across some oil next to the same bulldozer, that now looks completely different. (01:10:20)
Continuity mistake: After cutting through all the clone tubes in the incubation chamber, Dark Superman punches a console that controlled the clones' life support. In the close up of him hitting it, the screen he punches is red, but the screen on the left side of the console is black. It then cuts to a far shot and now the screen on the left is red like the one he punched. (00:59:30)
Continuity mistake: When Lois sees Jimmy taking pictures of where Toyman was killed, you see him lower his camera to his chest, then down to his stomach. It cuts to a close up of him, and suddenly his camera is at his chest again. (00:49:15)
Continuity mistake: As their fight reaches the Superman Memorial Park, Dark Superman punches Superman down it and there is a bulldozer. The amount of dirt in the shovel of the bulldozer increases between shots. In the same shots, there is a large pile of wood next to the tanker truck that disappears as Superman is thrown into the truck. (01:10:00)
Continuity mistake: While Lois is going through Lex's computer, a drawer behind her shows several folders. All of them have white labels on the tabs. But moments later when Lois is shuffling through those files, the labels on the side she's going through have vanished. (00:56:00)
Continuity mistake: When Dark Superman stops by Le Fantastique Salon, he stops right by the door. Then he tosses the list Lex gave him in the trash and goes inside. But he has to walk a couple yards to get to the door, despite stopping right by it only a moment before. (00:52:45)
Continuity mistake: In the scene where Lex kills Tess, several shots of his desk, most prominently the silhouette of him shooting Tess through the window, show that he does not have any computer towers under the desk. Yet later when Dark Superman is walking into Lex's office and he confronts him about being out of character, there are now towers under the desk. (00:34:35 - 00:51:45)
Continuity mistake: When Lois confronts Jimmy outside the night club, Jimmy turns around and has his left hand cupping the underside of the lens on his camera. When the camera angle changes, his hand is suddenly gripping the side of the camera. (00:44:25)
Continuity mistake: As Superman is returning Lois to her apartment after rescuing her from Toyman, he goes to land on the balcony outside her room. It is first shown as small with only a table and one plant on it. But as soon as Superman lands, it is suddenly a lot bigger and a lot more stuff is on it. (00:39:25)
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