The last scene shot for the film was one of the best and was not in the original script -- the Lois and Superman reunion flight and discussion on Clark's balcony. Reeve wrote this scene himself on deciding that the film was missing a mature Lois/Superman moment.
Superman IV was the only film in the series that was not produced by Alexander and Ilya Salkind, who by 1987 had turned their attention to a syndicated television program based on the adventures of Superboy.
An entire storyline was written out of the film where Luthor's first attempt at creating a Nuclear Man is a resounding failure. Nuclear Man I, as he was known during filming, makes his debut at the opening of the Metro Club. Clark and Lacey are there and that is when Nuclear Man I spots Lacey for the first time. Nucear Man II has the memories of Nuclear Man I and that explains the attraction to Lacey at the end of the movie. Superman battles Nuclear Man I outside the Metro Club and destroys him. Lenny Luthor secretly gathers the genetic remains of Nuclear Man I so that Uncle Lex can try again.
When Nuclear Man destroys the Great Wall of China, Superman was supposed to rebuild it at super speed according to the script. When the money problems emerged, Superman used his "Great Wall of China vision power" to repair the Wall. This required only that the director run the camera in reverse rather than a complicated super-speed scene.
The original theatrical print had Nuclear Man converting himself into a nuclear missle in an attempt to fool the world into thinking someone had detonated a nuke. Nuclear Man intended to destroy the world leaving only himself and Lacey the survivors.
Little Jeremy and Superman only meet once in the final print of the film. Two scenes were cut from the final print where Superman interacts with Jeremy. First is a scene where Superman replies in person to Jeremy's letter. And then, after his press conference at the end of the movie, Superman picks up Jeremy to fly him around the world so that he can tell the people of Earth that, from high up, you can't see borders, just one world.
The vast majority of the external scenes in this film such as the U.N. building in Metropolis were filmed in and around the town of Milton Keynes, Bucks, England. This was due to the Cannon producers Menahem Golan, Yoram Globus refusing to budget a shoot in New York City.
After Clark hits the baseball into space (while in Smallville) we see a flashback sequence of Krypton with the faded images of Marlon Brando and Susannah York), with a voice over(presumingly Jor-El, but due to it being another studio, they couldn't get the audio). Clark than wakes up in Metropolis as Lois calls him to tell him Perry wants to see them. Clarks goes to pick up the phone, but is too late. Than the scene goes into Clark walking out of his apartment and being greeted by a Daily Planet reader and her dog (named Godzilla) either attacking or playing with Clark until he rushes back in the apartment.
A scene in which Superman arrives at Jeremy's class to tell him why he can't help him(in response to his letter)because he had vowed never to interfere in the destiny of the planet (which was told to him by Jor-El in his ship)while all the kids are in awe. (This scene I assume takes place right before Jeremy's disappointed Press Conference)The beginning of the scene shows unfinished flying FX.
After finishing with making a cell from Superman's piece of hair, they attempt to clone Superman. Before "Nuclear Man" was made Lex and Lenny had a failed experiment. This is referred to as "Nuclear Man 1" and without resembling Superman has many characteristics as "Bizarro. " This "Bizarro is very childish, this scenes shows Lex shooting at him, making him break steel and fly (and crashing). The scene ends with Lex telling him to destroy Superman. Audio from this scene is heard in the film, while Lex and Lenny are making the cell.
The previous scene continues with Nuclear Man 1 scaring off a hooker (who was hitting on him) and Superman coming out where they have a small fight. This fight ends with Superman throwing him into an eletrical box and exploding to ashes (throughout the fight he attempts to reason with him). The scene features stupid sound FX and you can tell they're not hurting each other since the editing wasn't finished.
The next cene shows Lenny bringing Lex the ashes of his 1st Nuclear Man. Lex than realizes that he needs more than simple radiation and needs to use the sun. He talks it over to his manucrist and figures out that using one of the rockets Superman throws into the Sun is the best thing.
A scene making more sense out of Lex's scheme, shows Lex visiting both the US and the enemy and convincing both sides to buy his War weapons (thus why he has made so much money later) and than showing both sides buying up.
After Nuclear Man II kidnaps Lacey he brings her to Lex's suite. The scene jumps to Lex yelling at Nuclear Man II to awake from sleeping. Lex than reveals that both sides are ready to begin bombing. NMII than makes a pass at Lacey who slaps him and he walks out to "Have some fun. " Lex tells NMII that if they bomb each other they all will die except him. NMII than spins himself so fast it appears on both sides blips as the other side has launched a Nuclear bomb and they get ready to launch a missile. Than as Lex and Lenny try to leave, Superman arrives to ask Lacey to help by using her as bait by taking Lacey and making it seem like she is in trouble causing NMII to go back to norma and the blip to disappear. (Bad FX in this scene).
An extention of Superman's speech at the end, with various places hearing Superman's speech. Superman than flies over the world with Jeremy(who he picks up from school again). Superman ask Jeremy what does he see and he replies that he what he sees, but there's no borders just one world. The scene continues with Superman flying past the Russian spaceship he saved in the beginning before making his traditional ending of a Superman film. (Bad flying FX)
In the uncut version of "Superman II", Superman destroyed the Fortress of Solitude at the end of the film because its secret location had been discovered by Luthor. The Fortress reappears in Superman IV. It is completely bathed in green light unlike its previous ice-white look.
The syndicated television broadcast of Superman IV added 3 minutes to the film's 89 minute running time. First is a scene where Nuclear Man causes a tornado in the Midwest and Supes saves a little girl who is pulled into the tornado's vortex. The little girl is played by Reeve's daughter. The second added scene involves Nuclear Man flying to Moscow during the big battle scene and attempting to detonate a nuke in Red Square, which Superman is able to prevent with his super-breath.