Like the original Zone, this Zone is a water-filled underground system with fans and blocks. Interestingly, Act 1 uses Act 2's original background and vise versa. In the background Act 2, some of the walls are also shown to have crumbled, revealing large cathedral windows.
After escaping Little Planet, Sonic, Tails and Knuckles drop into Hydrocity Zone during their mission to get the Phantom Ruby away from Dr. Eggman. Midway through the Zone, the team gets back at Eggman with his own Egg Mobile when he tries to escape them. Sonic and co. also manage to escape Eggman's final trap at the end of the Zone, although the egg-shaped scientist again eludes capture.
The majority of Hydrocity Zone is underwater, so this requires the player to go slow and steady. Most of the new Zone designs and concepts are implemented in Hydrocity Zone Act 1. This Act's main gimmick is a mechanic that allows the player to control the local water levels by pulling down green Switch-based hooks that hang from the ceiling. By manipulating the water levels, players can utilize gimmicks like canoes to cross pools and reach new paths. In the underwater sections, there are also Switches that encapsulate the playable characters in Air Bubbles that they can ride around in underwater. While riding these bubbles, players can press left/right to steer them, press up to ascend faster, and press the jump buttons to escape them. The underwater sections also have fans in several spots that create currents the player can ride (both with and without an Air Bubble), which are often necessary to reach certain areas.
Hydrocity Zone has several underwater passages that suck the playable characters into them. Within them, the player has no movement control, although they can avoid obstacles by moving up/down the fragile poles that the characters occasionally grab onto when passing through. Some areas also have spears that periodically pop out of the surfaces.
Hydrocity Zone Act 2 features all the original gimmicks and elements from the original Hydrocity Zone Act 2, except for the moving wall and the inclusion of downard underwater currents.
Act 2 is more straightforward in design in comparison to Act 1, being based on Act 2 of the original Hydrocity Zone, with some level design incorporated from the original Hydrocity Zone Act 1.
The boss of Hydrocity Zone Act 1 is Dive Eggman, who is Dr. Eggman in a scuba suit. The battle "begins" with Eggman deploying bombs that cause the water level to rise, initiating a short segment where the player must reach an Egg Mobile with the Waterspout and Depth Charge attachment before getting crushed in between the rising ground and the ceiling. The player must use the Egg Mobile to suck up Eggman and damage him with the machine's blades while avoiding sucking up the bombs he deploys. The depth charges can be used to destroy the bombs though. After four hits, Eggman will be beaten.
The boss of Hydrocity Zone Act 2 is the Laundro-Mobile, an underwater vehicle used by Dr. Eggman. The battle begins with Eggman using a propeller to blow the player rightwards underwater. During this phase, the player must avoid spikes while activating bombs. Hitting Eggman with the bombs damages him and produces an air bubble for the character to stave off drowning during this phase of the battle. After six bombs have hit, the battle changes to a regular platforming battle that mimics the Whirlpool Machine from the original Hydrocity. After eight hits, the battle is over.
- This is the only Zone in Sonic Mania to originate from Sonic the Hedgehog 3.
- Normally when playing through original stages in Sonic Mania, the first act is a slight remake of the original stage and the second act is a complete remake. However, Act 1 is completely remade, while Act 2 is a slight remake of Hydrocity Zone's Act 2.
- The prediction of Hydrocity Zone being in Sonic Mania started from a tweet from Lucas Carvalho on Twitter. He made a picture of Knuckles running through Hydrocity, but it was later deleted and changed to Flying Battery Zone.
- Hydrocity Zone has the largest amount of Badnik types in Sonic Mania, at seven.
- Hydrocity Zone features several references and Easter eggs:
- The spear obstacles in Hydrocity Zone Act 1 and 2 are taken from the Labyrinth Zone in the original Sonic the Hedgehog.
- The Jellygnite, an enemy that appears in Hydrocity Zone Act 1 and 2, originates from Hidden Palace Zone in the remake of Sonic the Hedgehog 2,
- In Hydrocity Zone Act 1, there are levers which are used to open up for new areas. These objects are seemingly based on the same gimmick from Mystic Cave Zone in Sonic the Hedgehog 2.
- The water passages with strong water currents in Hydrocity Zone Act 1 are seemingly based on the same passages from Tidal Tempest in Sonic the Hedgehog CD.
- The ridable Air Bubbles in Hydrocity Zone Act 1 are based on the same objects from Aqua Lake Zone in the 8-bit version of Sonic the Hedgehog 2.
- The rising ground segments before the fight with the mini-boss in Hydrocity Zone Act 1 are based on the same occurrences from Marble Garden Zone/Flying Battery Zone in Sonic & Knuckles.
- The Dive Eggman boss fight in Hydrocity Zone Act 1 is a reverse of the boss fight from the original Hydrocity Zone Act 2 in Sonic the Hedgehog 3, with the player using Eggman's vehicle to attack the doctor.
- The Laundro-Mobile is based on Doctor Robotnik’s Whirlpool Machine from the original Hydrocity Zone Act 1 in Sonic the Hedgehog 3. The same goes for this boss fight's second phase.
- A secret feature can be unlocked in Hydrocity Zone by performing a specific set of actions. While hanging from a hook, input the following command: ← ← ← → → → ↑ ↑ ↑. This is the same code used to activate the Level Select in Sonic the Hedgehog 3 & Knuckles and Sonic & Knuckles in Angel Island Zone and Mushroom Hill Zone respectively. Upon successful entry of this code, the sound effect of a Ring will play. This code changes the sound effects produced by the speed boosting machine to , specifically from his video in which he yells "SHEEEE YEH!" when using a speed boost machine.
- This cheat code was removed in the version 1.03 (Xbox One and PS4)/RC 1.03.0919 (PC) update released on September 2017.
- The Sonic statues that appeared in Act 1 of the original Hydrocity Zone are now found in Act 2 (since the backgrounds themselves are swapped over from the original). These statues are also based on Sonic's sprite used in Sonic Mania, which is based on his sprite from Sonic the Hedgehog 2.
|Hydro City Zone (Act 1)||Tee Lopes||0:56|
|Hydro City Zone (Act 2)||Tee Lopes||0:59|