Metroid II: Return of Samus DX

About

Metroid II: Return of Samus DX is a rumored Game Boy Color port which was never released.

A screenshot was featured in the German gaming magazine "Club Nintendo" that was claimed to make use of the Game Boy Color's vast color-palette. However, the game never released and its existence has been contested by a testimony from Nintendo of America translator Dan Owsen who was unaware of plans for the port, suggesting that the screenshot featured in the magazine may be a mock-up.

Source: IGDB