I didn't want to open a whole thread just for this, but I don't really know where to post it.
There is an enemy who looks very similar to Marx in the game Trip World for Gameboy.
Look at 9:30 of this video.
(if the youtube tag doesn't work)
The enemy can be defeated, and you can walk on the ball after defeating it. The ball rolls and moves as you walk on it.
Trip World predates Kirby Superstar, Trip World is from 1992, while Kirby Superstar is from 1996.
Do you think that it's possible that Sakurai or someone in the development team took inspiration from Trip Wolrd for the design of Marx? (at least the pre-bossfight design).
This situation reminds me of how freeing the People of the Sky from those cages in Triple Deluxe and using the Robobot Armor in Planet Robobot seem to be inspired by some very similar gimmicks from the game A Boy and his Blob (the Wii remake, not the original).
Do you think that there are other game elements inspired by other games in the Kirby series? Such as, still in Trip World, you can transform into a ball, and the controls are suspiciously similar to Ball Kirby from Kirby's Adventure, even though the two games were released very close to each other so it's probably just a coincidence (unless some trailers of one of the two games were released many months before).