Special Stage (Sonic Triple Trouble)
From Sonic Retro
Sonic Triple Trouble. To access them you have to hit an Emerald Monitor () while you have 50 or more rings, and jump in the circle of stars that appears. The Emerald Monitors are hidden in Act 1 and 2 of every Zone.
There are two kinds of Special Stages: 2D Stages and 3D Stages (as they are referenced on the manual).
The first, third, and fifth special stages take place in a maze where you have to find your way up to Nack the Weasel, who acts as a boss, trying to prevent you from collecting the Emerald. However, in the first stage, Nack doesn't fight you, as the button he activates backfires against him. You have one minute and thirty seconds to reach Nack (the fight itself seems to have no time limit), but there are Time Monitors () to help you on your way.
The second and fourth special stages take place in the sky, respectively during day and during night. You have to drive an airplane and collect 80 rings while avoiding the bombs, in a fashion similar to the special stages in Sonic 2 for the Genesis. When you collect the 80th ring you are warped in an arena, just like the ones in the 2D stages, where you fight against Nack the Weasel.