SEGASonic Bros. (found unreleased arcade puzzle game; 1993)
SEGASonic Bros. was an arcade game that was never properly released. It was a puzzle game where Sonic is joined by red and yellow recolors of himself with differing personalities, the red one being cheerful, and the yellow one more brooding/shy. In the game, the player must stack Sonic's copies (multi-colored orbs) together to earn points, similar to Cleopatra Fortune.
The game was designed by Fukio Mitsuji, and given a location test. It failed this test, and was never released, possibly being marked as one of two unsatisfactory Sonic arcade games in a press release. The game fell into obscurity for many years until Custom Robo's creator Kohji Kenjoh brought it up 20 years later, followed by a few Twitter posts on the game.
The game was found by "ShouTime", an arcade board collector. He has yet to dump the game online, however.