Bonus Stage (Sonic 3D: Flickies' Island; Saturn/PC)
From Sonic Retro
The Special Stage, in Sonic 3D for the Saturn is more strictly tied to the Sonic 2 half-pipe special stage format than the Mega Drive special stages. This version uses true 3D effects, as well as tunnels, springs, and dash zones, though with what is often considered a lower difficulty than the originals. As usual, rings are collected and collecting a minimum amount rewards the player with an Emerald.
The PC stages also take, place in a half pipe but only have a single stage and copious amounts of rings that lead to a lack of difficulty in the stages.
To access those special stages the player has to find either Tails or Knuckles in the regular levels, and touch the characters while carrying at least 50 rings. Note that the ring count is set back to zero when entering a special stage. A ring bonus is awarded for those rings at the end of the act. Tails' and Knuckles' special stages only differ in their appearance. Between the two special stage settings, there are fourteen special stages, but only seven emeralds to collect: the player is given the choice to collect each emerald in the kind of stage they prefer. Collecting all seven emeralds will not unlock Super Sonic, and is not required to complete the game. It is required, however, in order to access the Final Fight and see the good ending.