One of the spin-offs of Mego's "World's Greatest Superheroes" action figure line was Mego's "Bend N Flex" bendies line! Along with the superheroes, Mego did Planet of the Apes bendies, too (I don't believe they ever did Star Trek or Monsters Bend N Flex figures, which is kind of a surprise).
Here's some photos of the whole line, and as you can see, all these were also done as 8" figures.
Superman was represented, as you can see, by Superman, Supergirl, and Mr. Mxyzptlk. Here's Mxy on the card:
And a better look at Supergirl:
There were even variations on the card art, as you can see by Superman above!
Not a bad-looking line... but I suspect it didn't do all that well, as some of the later Megos weren't represented in bendy form!