Name: Tetris
Platform: Sega Genesis / Mega Drive
Region: Japan
Media: Cartridge
Controller: Gamepad
Genre: Puzzle
Gametype: Prototype
Release Year: 1989
Developer: Pageantsoft, Dr. Pepper Studio
Publisher: SEGA
Players: 1
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So you think the unlicensed Tetris game for the NES is hard to find? Just try to get your hands on the Japanese Megadrive Tetris. It was developed alongside Sega's System-16 arcade version, but never reached shelves after legal wranglings gave Nintendo exclusive console rights. However, that little issue doesn't stop some people from obtaining it. Apparently, there are about 10 copies known to be floating around.

http://www.racketboy.com/retro/sega/genesis/2008/06/the-rarest-and-most-valuable-sega-genesis-megadrive-games.html