Mad Gear Zone

Mad Gear Zone is the fourth and penultimate zone of Sonic the Hedgehog 4: Episode I. As Dr. Eggman's headquarters, Mad Gear is a mechanical death-trap factory surrounded by steam pouring pipes, cogs and gears to balance on.

Website info
A huge plant constructed by Eggman to turn his maniacal ambitions into reality. This is Eggman’s final fort filled with violently moving pistons, giant gears, high-pressure steam valves, and deadly badniks. Sonic will need to master all of his skills effectively to survive.

Title(s)

 * Act 1 - Dr. Eggman's Secret Base
 * Act 2 - Escape the Cog Trap
 * Act 3 - Impending Doom
 * Boss - Defeat The Real Dr. Eggman

Prologue
Defeated yet again, Eggman hastily retreats from the tricky trap labyrinth and heads directly east to his home of operations in his personally-built metallic city. Unbeknownst to him, Sonic sees the sneaky doctor worm his way out of the ancient maze to his base. With the element of surprise on his side. Sonic heads toward the evil metal city to confront his arch-nemesis once and for all.

Act 1 - Dr. Eggman's Secret Base
After sneaking in Sonic soon discovers that the base isn't so safe or hedgehog friendly. Taking in all his past experiences he blasts forward, wholeheartedly aware he's in the lion's den. Running through, Sonic finds that steaming pipes can give him a boost if he needs it, or lift him into an untimely spike death. This is coupled with the fact that old enemies return to give him more trouble. At last, they do not slow him down as he whips through the zone finishing the first descent.

Act 2 - Escape The Cog Trap
Running past all the traps, Sonic finds that sneaking in is harder than it looks as he finds himself jumping, hopping, and running on and off cogs, bolts, and gears throughout the base. Sonic will have to balance on gears to get to the next part of the the base.

Act 3 - Impending Doom
By this time, Eggman realizes that Sonic's been here for sometime and takes extreme cautionary actions by shutting down the exits ahead as the stage goes dark and alarms from the glowing red lights go off. Eggman also limits the time for Sonic to find an exit by having a wall full of saws give chase and make sure Sonic never survives.

Boss - Defeat The Real Eggman
Sonic finally meets up with Eggman as he floats down with yet another previous invention; this time around, Sonic can hit the pods, which causes them to deploy a balloon duplicate of Robotnik's self, but when Sonic tries to attack the balloon, he gets hurt; a direct contrast to the original after losing all his pods. Eggman will then flee, but Sonic quickly runs after him in this second phase as he throws small fast and blue ones, and very large yellow ones. After taking a few hits, he will be defeated.

Sonic the Hedgehog 4: Episode Metal
Flying straight from Little Planet after being reactivated, Metal Sonic arrives in a sorry state at Mad Gear Zone, discovering that Doctor Eggman was waiting for him. Eggman beckons Metal into his machine, powered by the entire facility, which then repairs and enhances Sonic's robotic double, thus revealing the purpose behind the mechanical city's creation. Reborn, Metal Sonic takes off to locate Sonic and destroy him.

Act 1 - Metal Sonic Returns!
The stage is a reworked version of "Act 1 - Dr. Eggman's Secret Base" from Episode I, bearing an altered level design, a higher amount of enemies, and more spikes and traps.

Trivia

 * This zone is based on Metropolis Zone from Sonic the Hedgehog 2 (having Slicers, Shellcrackers and Asterons as enemies), with some ideas taken from Scrap Brain Zone from the game Sonic the Hedgehog (1991).
 * The first phase of the boss fight is also inspired by Metropolis Zone, but the second phase appears to take ideas from Mushroom Hill Zone, having to run after Eggman across a course that only ends when the fight does.
 * Mad Gear Zone was leaked with a video of Act 2, revealing Super Sonic will be playable in the game.
 * Some of the cogs you can run on in Act 2 work similarly to the screw elevators in Metropolis Zone.
 * It's said on the Sonic the Hedgehog 4: Episode II website that Eggman built Mad Gear for some reason that makes it connect to Episode II's plot. This reason is to give Metal Sonic enough power to retrieve the orb in Lost Labyrinth, as is shown in Episode Metal.