Sonic & Knuckles features "lock-on technology" that allows players to open the hatch on the cartridge and insert a second cartridge. When Sonic 1 is inserted, the result is a deceptive "No Way!" screen. However, by pressing the A, B, and C buttons together, players can access a minigame based on Sonic 3's and Sonic & Knuckles's Chaos Emerald Special Stages (known as the "Blue Sphere" game). All of the possible variations of the special stages are now available to play, each with a unique level number and corresponding password.
