Metropolis Zone is the eighth zone in Sonic 2. It is an extra-long level in which Dr. Robotnik resides. There are lots of machines, including the Pipe Teleporter and screw elevators, as well as pistons that vent steam from the sides. Dr. Robotnik protects himself against Sonic with spiraling eggs, each containing a fake Robotnik in the boss.
Metropolis Zone has 3 acts, like all zones of Sonic 1 (save Final Zone). However, all the other zones in Sonic 2 have two or one. This is because Tom Payne (the artist in charge of this level) had also been assigned another level that was finally scrapped due to lack of time in favor of this third act.
Mad Gear Zone from Sonic the Hedgehog 4 seems to be based on Metropolis zone. Mad gear has all three badniks from Metropolis: Asteron, Slicer and Shellcracker. Also, the first part of the boss fight is the same as Metropolis Zone's boss.
Sonic's finally chased Robotnik to his own capital city. But he finds a fortress of iron and steel. Danger lurks in every spinning cylinder, pounding piston and rolling gear. Hold the D-Button RIGHT or LEFT to wind the nut up and down the screws.
Sonic Team Commentary (from Sonic Jam Strategy Guide)
“
Due to problems with the story, Act 3 was going to be a different Zone that would only appear once, but since it was cut, we still wanted to have something after Act 2. So that's why there are three acts in this one. We had already finished the map, and it would have been a shame to waste it, so this is what we went with.
Unlike almost every other level in the 8/16 bit games, Metropolis Zone loops from top to bottom. There are several areas (most notably in acts 1 and 2) where you can fall seemingly forever and load up on speed and rings.
Enemies
Asteron - Starfish enemy, explodes when you go near it, launching 5 small spikes outwards.
Slicer - Mantis enemy, throws two blades at Sonic.
Shellcracker - Crab enemy, extends its giant claw towards Sonic. Referred to as "Shellcraker" in Sonic Jam.
These are cheat codes which can be accessed by inputting button sequences or by various other methods.
Note: in cheat codes, + signifies that the buttons must be held simultaneously.
Zone Select: Play tunes 19, 65, 09, 17 on the options screen, + on title screen.
14 Continues: Play tunes 01, 01, 02, 04 on the options screen. An incorrect sound command is issued, causing OOZ music to continue playing until a reset.
Super Sonic: Play tunes 04, 01, 02, 06 on the zone select sound test, an emerald sound triggers, select zone, hold until Sonic appears.
Debug mode + Slow-motion/Restart: Play tunes 01, 09, 09, 02, 01, 01, 02, 04 on the zone select sound test, a ring sound triggers, select zone, hold until Sonic appears.
Super Sonic + Debug: Play tunes 01, 09, 09, 02, 01, 01, 02, 04, 01, 02, 06 on the zone select sound test, a ring sound triggers after 04 and an emerald sound triggers after 06, select zone, hold until Sonic appears.
