Superman: Battle for Metropolis – The Unreleased Game Boy Color Prototype Superman: Battle for Metropolis is a Game Boy Color game that never made it to shelves — an unfinished prototype that gives a fascinating glimpse at what a GBC Superman title could have been. It exists solely as a development build, and this cartridge lets you experience it on real hardware exactly as it was left. Custom cartridge, plug and play. Compatible: GBC, GBA, GBA SP.