From Sonic Retro
Cosmic Wall is the thirteenth stage of the Dark story and Dr. Eggman's fifth and last. It is unique in both the fact that it is the only level to have its A-Rank requirements changed from the Dreamcast to the GameCube and in its low gravity conditions.
After learning of Sonic, Tails, and Knuckles' arrival on the ARK and Tails' fake emerald, Eggman plans to confront them and get the real 7th emerald, while leaving Shadow behind in case something happens.
At end of the level Eggman has a final confrontation with Tails.
Eggman first starts in a staircase like platform section, which is easy to overcome by jumping and using hovering to reach higher places thanks to the lower gravity. Halfway up and after the platform with a crusher, there is the first Point Marker.
After this the section continues likewise the previous part, though there’s some pyramid like boxes that block the way, that can be destroyed by shooting at them. Past some of this there’s the second Point Marker. Here and in the next platform, there’s a platform to the right, with a Mystic Melody. Activating will make a spring appear, which will launch Eggman to a series of square platforms higher and higher, some with meteorites, until a ledge in the ARK. Back at the beginning platform, there’s more of the same from the previous sections and at the end close to the ARK there’s a shaft with various square platforms that Eggman needs to climb. Halfway to the top there is an upreel that takes to some more square platforms and finally there’s a spring, that launches Eggman to yet another shaft section like the previous, but this time, it needs to be descended. Halfway down there’s a missile that destroys some cages to the right, where Eggman’s Protective Armor upgrade is. Finally at the bottom there’s a room where the third Point Marker is.
Beyond there’s an on-rails section, with the Egg Walker attached to a platform that moves through a monorail. There’s a lot of enemies and enemies to destroy, awarding a lot of combo points if locked on simultaneously. At the end there’s a similar room from where Eggman first came from, and the fourth Point Marker.
After there’s another ascending shaft with square platforms, and at the top another descending shaft, but with only one platform halfway done, with ring boxes. At the bottom there’s the fifth Point Marker.
Beyond there’s a platform section equivalent to the first section of the level but with the platforms more spaced from one another horizontally. Nothing here is very different, save for a platform with some rotating spikes and a crusher switch combo, but it’s not needed to manipulate to reach the higher level. At the end of the staircase section there is a horizontal path with some platforms amongst meteorites and the sixth Point Marker.
After this there’s yet another ascending shaft with square platforms, some upreels and another descending shaft with enemies only and after a hallway, the seventh Point Marker. Beyond there’s another on-rails section similar to the first but larger, then a tunnel with a motor chasing the platform and with six bullets that can be destroyed, and after this Eggman is launched to the Goal.
The level specific animal (third Chao container) is a Unicorn.
After boarding the final rail ride, keep a sharp eye. The first time the rail ride passes under a platform with laser turrets on it, Big will be directly above that point, hiding behind a laser turret. It may be easier to spin the camera around and view Big from behind after you've passed the platform, but you still have to be quick in any case.
The Gold Beetle can be found when you encounter the first Hornet-3. Jump off the railing to the left and hover to ascend slightly further than the Mono Beetle.
Differences between Dreamcast and GameCube versions