When you initiate Sonic The Hedgehog 1, 2, 3, Sonic And Knuckles, Sonic 3D blast, Dr. Robotnic's Mean Bean Machine, or Sonic Spinball, the screen states that it is logging the game data. That indicates the game is logging in that you have initiated that game once. After initiating a game fifty times, it no longer shows that game-logging screen. It stops the logging sequence screen from ever starting a game again and from then on, just starts the Genesis program itself. To unlock a hidden game, you must start a particular Mega Collection game fifty times, continually pressing Z to exit it, then enter into the game repeatedly. Some hidden games do not necessarily require that you start up fifty times, but you eventually need to do so to unlock all the hidden games.
Flicky: Start Dr. Robotnic's Mean Bean Machine before reaching 50 times.
Blue Spheres: Start Sonic The Hedgehog about 18 to 21 times
Sonic 3 And Knuckles: Unlocked sometime in the process of starting Sonic 1, Sonic 3, Sonic And Knuckles, and Sonic 3-D Blast fifty times.
Knuckles In Sonic 2: Unlocked in the process of starting Sonic Spinball and Sonic 2 fifty times.
Ristar: Start all games (Sonic 1, 2, 3, Sonic And Knuckles, Sonic 3 And Knuckles, Knuckles In Sonic 2, etc.) fifty times.