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 (character) "Sonic & Knuckles", both released in 1994, saw Sonic and Tails battle Robotnik again, with the additional threat of Knuckles, who is tricked by Robotnik into thinking Sonic is a threat. "" (2010–2012) continues where the story of "Sonic 3" left off, reducing Sonic to the only playable character and releasing in episodic installments. The second episode sees the return of both Tails as Sonic's sidekick and Metal Sonic as a recurring enemy. Other two-dimensional platformers starring Sonic include "Sonic Chaos" (1993), "Sonic Triple Trouble" (1994), "Sonic Blast" (1996), "Sonic the Hedgehog Pocket Adventure" (1999), "Sonic Advance" (2001), "Sonic Advance