Monster Rancher Battle Card GB, released in the USA, adapts the popular Monster Rancher franchise to a card-battle format. It probably involved collecting, training, and battling unique creatures. The adaptation of the game to the Game Boy Color would've included simplified controls and game mechanics to accommodate the handheld system's constraints.  The details of the game's specific mechanics and its developers would require further research.

Monster Rancher Battle Card GB (USA)

Monster AG, Die (Germany)