|Hydrocity Zone (Sonic Mania)|
|Seventh level, Sonic Mania|
|Number of Acts: 2|
|Level theme: underwater|
|Secondary level theme: underground/cave|
|Boss: Laundro Mobile|
|Sub-boss: Dive Eggman|
Unlike most other returning zones in Sonic Mania, Hydrocity is designed in that all the new level designs and ideas are presented in Act 1, with the main gimmick being the water level being controlled by the player by pulling down certain hooks hanging from the ceiling. By adjusting the water level, the player is able to use other features such as boats to cross the water. In underwater areas, there are buttons that will release giant bubbles that the player can ride in, much like in Game Gear titles like Sonic Triple Trouble. When riding the bubbles, the player can press or to move, to rise faster, and any of the jump buttons to get out. Fans can push the bubble around, which is necessary for getting through certain spots.
Due to the new ideas being employed in Act 1, Act 2 is more straightforward in design, being based on the original Act 2 while having some level design from the original Act 1. All the features you would come to expect from Act 2 return with the exception of the moving wall, and the addition of underwater currents that pull the player downward.
Curiously, the backgrounds are swapped between both acts, with Act 2's background now used in Act 1 and vice versa. In Act 2's new background, some of the walls have crumbled, revealing large cathedral windows.
|Reference||Appears in||Source Game||Source Level|
|Pop in/pop out spears.||Act 1, Act 2||Sonic the Hedgehog (16-bit)||Labyrinth Zone|
|Jellygnite's appearance.||Act 1, Act 2||Sonic the Hedgehog 2 (2013)||Hidden Palace Zone|
|Levers opening new areas.||Act 1||Sonic the Hedgehog 2 (16-bit)||Mystic Cave Zone|
|Water tubes with strong currents.||Act 1||Sonic the Hedgehog CD||Tidal Tempest Zone|
|Rideable giant bubbles.||Act 1||Sonic the Hedgehog 2 (8-bit)||Aqua Lake Zone|
|The rising ground segment before the mini-boss fight.||Act 1||Sonic 3 & Knuckles||Marble Garden Zone/Flying Battery Zone|
|The reverse mini-boss fight to the original Hydrocity Zone's boss fight featuring attacking Dr. Eggman with his own vehicle.||Act 1||Sonic the Hedgehog 3||Hydrocity Zone|
|Main boss's design based on the original Hydrocity Zone's Big Shaker along with the identical boss fight's second phase.||Act 2||Sonic the Hedgehog 3||Hydrocity Zone|
|Dunkey's Secret Sound Effect. (removed as of version RC 1.03.0919)||Act 1, Act 2||videogamedunkey||Dunkey's Best of 2016|
|Code to access the Dunkey secret sound effect is the same code used to access the level select in Sonic 3 & Knuckles. (removed as of version RC 1.03.0919)||Act 1||Sonic the Hedgehog 3 & Knuckles/Sonic & Knuckles||Angel Island Zone/Mushroom Hill Zone|