Game Boy

The Pocket Sonar by Bandai is one of the strangest accessories ever made for the Game Boy, and an officially licensed one. Built for anglers, it locates fish underwater. The chunky, battery-powered unit fits into the cartridge slot, and a float-equipped sonar hangs from a long cable, with a dry bag included to keep the Game Boy from getting wet.

The software adds a mini-game and a fish database for identifying the catch. It works with the original Game Boy and the Game Boy Pocket but not with later models.