As Sonic, the level is much longer. Sonic must jump from platform to platform, climbing up the Zone and chasing the newly risen Death Egg before it gets too far in orbit. Knuckles briefly helps Sonic by activating a bridge on the Sky Sanctuary, but he wasn't able to continue further to help due to exhaustion (presumably from Robotnik's earlier electrocution attack) Sonic must also battle numerous Eggrobos, which hover in place and fire lasers straight ahead when Sonic moves into view, and which can be defeated like regular Badniks. Sonic must also fight Mecha Sonic in this Zone, in three separate boss battles. In the first, Mecha Sonic pilots Doctor Robotnik's Egg Mobile-H (from the Green Hill Zone in Sonic the Hedgehog); in the second, the robot pilots the whirling bubble-pod mobile from Metropolis Zone in Sonic the Hedgehog 2. In the third battle, Mecha Sonic attacks on foot, without assistance. After this final battle, Sonic runs up a corkscrew ramp to the top of a tall floating landmass that crumbles beneath him, then leaps aboard the Death Egg (Note that, in Sonic 3 & Knuckles, playing as Tails will initiate Sonic's version of the level).
As Knuckles, this is the final Zone of the game, and consists of two boss fights against Mecha Sonic. The level in itself is very short, with only three Rings to help see Knuckles through the fights. The Zone is very small - just a flat, boss arena - after most of the Zone fell apart in Sonic's storyline. In the second fight, Mecha Sonic uses the Master Emerald to enter its Super State. Knuckles must race to gain back the Master Emerald for Angel Island, which is actually seen to sink in the background as the battle progresses. After Mecha Sonic was defeated, his destruction was severe enough to destroy any remainder of the Sky Sanctuary Zone, with Knuckles barely escaping, thanks to a timely assist from Sonic and the Tornado.
All three of the fights with the Mecha Sonic bear some similarity with bosses in earlier games, although the second fight is made much easier by the Insta-Shield move, something which Sonic did not have when facing the original version in Sonic the Hedgehog 2. The last battle with the two Sonics on foot can be likened to the fight with Mecha Sonic in the Death Egg Zone in Sonic the Hedgehog 2.
If the player plays this Zone as Sonic and/or Tails and crouches at a certain location after Knuckles activates the bridge, Knuckles will make a "shooing" gesture at the player's character(s) before turning to the player him/herself.
If you finish the stage with a shield power-up, notice that when Sonic leaps off the corkscrew, his sprite is just left suspended barely off screen, and half of his shield will remain visible in midair.
In Knuckles' story, the longer you take to beat Mecha Sonic, the more the island in the background falls. At 10 minutes, which is the normal time limit, the island just disappears under the Sky Sanctuary.
In the Sound Test option, the Knuckles and Sonic (and Tails) version of the Zone is separated by two acts.