SNK published "Crystalis" for the Nintendo Entertainment System console in 1990, an original role-playing game for the NES at a time when most of SNK's titles were conversions of its arcade games.  It's a very playable action RPG with a sense of humor and a solid story, as well as some fun nods to the rest of the SNK character universe.

TESTED AND WORKING, cartridge only, no box or manual, just the cartridge and generic black plastic sleeve.  Cartridge label has some surface wear and light scratching but is otherwise in decent shape, clean and colorful, with no stickers on casing; back side label has a name written in felt-tip pen on the back.