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HydroCity makes an appearance in Sonic Heroes 2. Here, it has morphed, owing to almost entire disuse (a vitriolic Knuckles passes through the top of it when departing and visiting Angel Island), into a seething pile of ferrous oxide, metallic madness and contaminated water.
Five teams play HydroCity. At the start of the game, Sonic, Shadow and Silver of Team Sonic go for a walk at the start of their storyline which involves HydroCity. At the end of it, Knuckles runs into the three - in Shadow's case quite literally - and while SSS wish to quiz Knuckles on him apparently dating Shade, he instead asks that they have a word with Scourge, who Knuckles believes he caught smashing the Master Emerald. (In actual fact he was sneaking up behind it with the intention of nicking it when Team Eggman smashed it, causing Knuckles to blame Scourge.)
Team Archaic play it on their way to Sandopolis, where they had believed they would be able to play without interruption not realising that Tiara Boobowski was busy sunbathing there. Team Big's storyline begins on the Mystic Ruins North/HydroCity border, where Froggy escapes while Big was fishing; the entire team eventually play the stage once as an action stage later on in that storyline, though they play it with a slightly lower tide than usual. Team Covert play HydroCity as an action stage en route to Labyrinth Zone. Eggman Nega and Metal Sonic 3.0 play HydroCity en route to Gigalopolis, where Emerl is, and the entire team play it en route Great Turquoise Zone, while looking for a Chaos Emerald.