Retroactive Recognition: Late into the line's lifespan, Mattel held a contest for fans to design their own character, which they would then make into an official action figure (the plan never came through). The winner was Nathan Bitner, who grew up to design characters for the Halo series.
Saved from Development Hell: The winning character design from the contest mentioned above was never made for unknown reasons, though Mattel came through with every other promised prize. Finally the character, Fearless Photog, was made as part of the Classics line for the 30th anniversary of the franchise.
There were plans for a prequel to both MotU and She-Ra featuring an ancestor of the main characters, He-Ro. Yeah, those never saw the light of day, but He-Ro has recently been released as part of the MotU Classics toyline.
Similarly, Vikor, He-Man of the North, is a MOTU classics figure based on the earliest stage of what would become He-Man's design.
The Monogram figure kit line was almost cancelled in favor of another project (which didn't itself see the light of day): a 1/25 scale Dodge Diplomat police car.
There was to be a sequel series called He-Ro Son of He-Man, featuring He-Man's adopted son, but nothing came of it.
The original idea for Two-Bad was making one of the heads be a good guy and the other a bad guy. This was skipped and both were bad.
In the 2002 series, they were going to be part of the Evil Warriors from the beginning, until their origin story was considered for a later episode.
Contest Winner Cameo: In the DVD Commentary, Gary Goddard mentions how Mattel held a contest where the winner would get a role in the film, but they didn't tell them about this until very late in production, so the winner just got a cameo as one of Skeletor's guards near the end with his face hidden under a pig mask.
Doing It for the Art: The final sword fight between He-Man and Skeletor was filmed at the very end, after the money ran out. The director paid out of his own pocket to get that vital sequence filmed and have a finished movie, which is why the set and lighting change so dramatically just for the lions share of the duel.
Role Reprisal: The Mexican Spanish dub use the same voice cast from the animated TV series.
Troubled Production: The film went into production at the wrong time, as He-Man was slowly dwindling in popularity, Cannon Films was going bankrupt AND Mattel was having financial issues. It went from getting a slashed budget right before filming began to spending the entire back half of filming trying to convince the crew that paychecks will be in that day. Filming was officially shut down just before they could film the climactic sword fight and have a completed movie, the director had to wiggle in another two days of extremely calculated filming to do the bulk of the fight later that evening and then squeeze in another day a month later (on the directors dime) to get the final shots before the set was torn down. They designed the set with the intention of the final fight using all of it and were disappointed in the end result themselves.
What Could Have Been: There were plans for a sequel, which got as far as early production. However, due to monetary issues, Cannon Films lost the rights to the franchise, and the whole project, along with the Cannon's cancelled Spider-Man production assets, eventually turned into Albert Pyun's Cyborg.