Yu-Gi-Oh! Monster Capsule GB is a video game for the Game Boy Color. It has only been released in Japan. The game takes most of its inspiration from the manga's Monster World story arc and the Capsule Monsters stories, using both Duel Monsters and Capsule Monsters.
I didn't expect to enjoy this game as much as I did. I thought it would be more complicated to understand, but it wasn't. This game is kind of like Fire Emblem mixed with Digimon.