Back around the year 1999, Takara decided to revive their old line of toys called “Microman” so they reissued a lot of the old toys from the 70’s and started a new line of toys. These toys had an anime and manga to go with the relaunch. The Microman line also had 2 games, Chiisana Kyojin Microman which was an 3rd person action game on the PSX with the old toy and Chiisana Kyojin Microman: Generation 2000 which was a more clunky game for the PSX with voiced parts of the characters from the anime.
However there was a game in development for the GBC which seems to have never seen the light of day, probably due to the failing sales of the 1999 version toys and the declining interest in the anime/manga. Below you can see a proposed cover art and a few screens form the game.
Thanks a lot to Maverynthia for the contribution!