Sonic the Hedgehog platforming of the main levels. The 16-bit "Sonic the Hedgehog " consisted of a giant rotating maze, which many considered a major technical achievement. The most common special stages, however, were segments with the character running through a long tunnel to collect certain items. 3D "collect item" levels, as in "Sonic 3" and "Sonic & Knuckles", used the same perspective but had Sonic collecting all the blue-colored orbs on the surface of a giant sphere. Finally, "Sonic Advance 2" employed a 3D ring-collecting stage, and "Sonic Chaos" ("Sonic and Tails" in Japan) used a variety of gimmicks for its levels.
Sonic the Hedgehog 3 to it. Connecting the "Sonic 3" cartridge creates a combined game, "Sonic 3 & Knuckles". The lock-on function is available in some digital releases of the games, such as the Virtual Console service for the Wii. "Sonic the Hedgehog 3 & Knuckles" allows the player to play "Sonic 3" levels as Knuckles or "Sonic & Knuckles" levels as Tails or both Sonic and Tails. Other new features are the ability to collect Super Emeralds, unlocking new "Hyper" forms for Sonic and Knuckles and a "Super" form for Tails, improved save options, access to new areas that Sonic or Tails could