Revealing mistake: Right when the Metropolis fight is about to start, Superman flies to the Daily Planet and passes by a building. Check the pattern on the windows and you'll notice that the same small door on the left appears almost everywhere, revealing that a miniature was used.
Revealing mistake: The villains send cars flying through the air. This was achieved with detailed scale model cars in a scale model Metropolis. But in order to mimic the blown-away citizens they use cheap mannequins that move on some sort of conveyor belt. (01:43:50)
Revealing mistake: When the villains blow away the stuff in Metropolis, the fire hydrant falls down and reveals it wasn't fixed to the ground, a blatant prop.
Revealing mistake: At the Fortress, when the villains and Superman play the appearing/disappearing trick, there's a shot with 4 Supermen onscreen, a special effect which was achieved with stand-ins. The one in front of Zod, and especially the one next to Lois look nothing like Christopher Reeve.
Revealing mistake: When Luthor is about to climb up the balloon his bald cap wrinkles by his nape.
Revealing mistake: In the prison laundry, Luthor's bald cap is very noticeable, especially by his sideburns.
Revealing mistake: When the phantom zone explodes it is a cheap pencil drawing animation.
Revealing mistake: When Luthor and Teschmaker are in the balloon, in the wide angle they both become coloured green due to the blue screen effect.
Revealing mistake: When Superman launches the Eiffel elevator in space and he flies back to earth, a white rectangle surrounds him where his image was superimposed to achieve the flying effects. (The Ultimate Collector´s Edition Box Set).
Revealing mistake: When Superman grabs the antenna above the pram, part of the antenna disappears because of the blue screen effects.
Revealing mistake: As Zod and crew blow people and objects down the street, it is obvious in some shots that they're all heading toward a painted studio wall.
Revealing mistake: As Ursa slams the man's arm down, the section of the table their arms hit has been cut to make the stunt possible.
Revealing mistake: As Non lifts the car to get the shotgun, the front of the undercarriage has a pile of dirt it, possibly to hide the lifting device.
Revealing mistake: The Cosmonaut Zod meets first pulls at his supply line. As he does, if you look closely the black wire used to make the hose move is visible.
Revealing mistake: As the astronaut that Ursa meets moves, the wires used to make him float are visible.
Revealing mistake: In a close-up shot of the kid falling into the falls, one can notice the kid is just a dummy. Notice how his face is a lot paler than it was before. (00:39:35)
Revealing mistake: The hole that Non and Superman go through is already patched, as it's a different colour from the rest of the pavement (either from previous takes or to allow the effect).
Revealing mistake: During the Marlboro truck scene, Zod's stunt double has very noticeably longer, darker and bulkier hair, plus a thicker beard.
Revealing mistake: After coming out of the Marlboro truck, Superman grabs Zod by his feet. When he sends him flying away, Zod's been replaced by an obvious doll.
Revealing mistake: In the first scene when the villains are at the console, you can see Ursa's nose disappear, then reappear when Non walks behind her, then it disappears again. (01:44:30)
Answer: In the theatrical cut, nobody really knows why the green crystal restored his powers. However if you watch the Richard Donner cut, it is explained that the green crystal is a communication device that helps Superman talks to the residual essence/spirit/ghost of his father Jor-El. Before he died, Jor-El gave the crystal to his son. Jor-El anticipated that Kal-El might give up his powers, and he also anticipated that Zod might eventually escape the Phantom Zone, so Jor-El lets his son absorb the leftover energy of his spirit, thus restoring all his Kryptonian powers.
Matt Van Gogh