From the Super Mario Wiki
The Mini Classics are a series of Game & Watch ports released in 1998. They are smaller than the originals and have keychains, increasing their portability. Additionally, the Mini Classics can also serve as a clock. The games are identical to their original (Game & Watch) versions. Their appearance is that of a small Game Boy Pocket, only missing the Start, Select and B buttons and the cartridge slot. They have also a stand but it is missing in the dual-screen Mini Classics such as Donkey Kong.