Revealing mistake: As the astronaut that Ursa meets moves, the wires used to make him float are visible.
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 When he sends him flying away, Zod's been replaced by an obvious doll.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: When Non and Zod break in through the White House window, a black strap is seen attached to each one's body to help them descend safely.
Revealing mistake: When Zod throws a man against the wall in East Houston, the man goes through the wall into a truck. Before he crashes against the truck, wires holding him are visible.
Revealing mistake: When Zod and Ursa jump out of Perry's window they fall down, revealing its a stunt from a ground level window. The outside shots however, show them flying up and straight.
Revealing mistake: Before the villains change the faces on Mt. Rushmore, the original ones (which are a matte painting) have a greenish look. Definitely not like the real sculptures.
Revealing mistake: At the beginning of the movie, we see the three villains in front of several backgrounds. In most of these backgrounds, their outlines are fuzzy, indicating that they are actually standing in front of a green screen.
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