Snail Maze(1986)

Snail Maze is a 1986 video game by Sega, part of the Sega Master System. Instead of being released on a cartridge, it was built into the system's BIOS and could be played by starting the system without a game cartridge inserted and holding Up and buttons 1 and 2 simultaneously. The later "Master System II" model did not include Snail Maze, it instead included a built in Alex Kidd in Miracle World. Snail Maze was never released in cartridge or card format.