Play Daikaijuu Monogatari - The Miracle of the Zone II (Japan) Online

Daikaijuu Monogatari: The Miracle of the Zone II came out in 1999 for the Game Boy Color, developed by Hudson Soft. It was part of that late 90s wave of Japanese RPGs that tried to do something a little different on handhelds, with a focus on monster collection and fusion rather than just traditional heroics.

You control a young hero exploring a world overrun by strange creatures; your main goal is to recruit these monsters, combine them into new forms, and use them in turn based battles. The game plays out screen by screen, with plenty of dungeon crawling and occasional puzzle solving. It moves at a deliberate pace, and some of the fusion outcomes can feel unpredictable, even a little absurd. Wandering through its world, tinkering with monster combinations, gives the whole experience a curious, experimental feel.