The concept of Stretch Armstrong was pitched to many different movie studios in the 1990s and 2000s before ultimately Hasbro decided on making a cartoon.
If Unit: E had panned out, we would've seen the Flex Fighters far earlier, fighting alongside other Hasbro heroes.
Wingspan wears purple in early concept art, instead of green.
"The Rise of the Tech Men" originally featured a gag where Stretch accidentally pulls the pants from a Tech Man to reveal drawers that had Twilight Sparkle and Applejack from My Little Pony: Friendship Is Magic. However, the actual episode release has changed that to a more generic hearts pattern. The original can still be seen in the "Villains of Charter City" trailer.
Hasbro originally suggested a Distaff Counterpart to Stretch as one of the Flex Fighters' allies. In the final show, the female allies they gain over the first two seasons do fight evil with Flexarium, but for different purposes than stretching.
The tie-in comic book to the series was originally going to have a second three-issue arc that took place between "Singularity Event" and "Crisis at the Cleo", but the comic seems to be cancelled after the first arc. Also, the comic was supposed to introduce a villain before the show, but this didn't come to fruition.
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