Mushroom Hill Zone

"Fantastic mushrooms cover the lush hills deep in Floating Island's interior. Many useful kinds of plants grow here. See how they can help you."

- Instruction manual

Mushroom Hill Zone is the first zone in Sonic & Knuckles (and the seventh of Sonic the Hedgehog 3 & Knuckles). It is a lush forest notable, as its name would suggest, for giant mushrooms that can be used as various springs and platforms.

Act One
In the first act, when playing as Sonic, Tails will airlift Sonic down from the free-fall after stopping the Death Egg's launch. Sonic then spies Knuckles closing the door to a passageway leading to a Warp Ring for Special Stage. In the complete game, Knuckles is hiding a glowing Giant Ring that takes the user to the island's Hidden Palace. Here all collected Chaos Emeralds' powers are halted by the Master Emerald and they are transformed into dormant Super Emeralds. From this point on, Giant Rings (distinguishable by the colors of the Emeralds which it flashes) transport the player to the Hidden Palace Zone for another chance at a Super Emerald. Mushroom Hill Zone contains lots of Warp Rings compared to other zones in Sonic & Knuckles, making it important to collect as many Emeralds as possible before leaving this zone if aiming to collect all seven before completing the game. When playing as Knuckles, he's seen relaxing and enjoying his playful friends when an EggRobo appears and tries to destroy Knuckles with a well-placed bomb. Knuckles gives chase and the game proceeds often with secondary paths not available to Sonic and Tails. In Sonic the Hedgehog 3 & Knuckles, this event does not occur, and the EggRobo instead throws the bomb at the end of Launch Base Zone.

Act Two
The second act takes place on a desperate run through the forest to stop Dr. Robotnik from destroying it by means of a weather machine that rapidly progresses the seasons from spring, through summer and autumn and into winter. Through different sections, the color of the forest will change from green to red to tan. At the end, the player must destroy the weather machine (in the form of a satellite dish in the ground) to turn the forest back to green and trigger the boss fight.

Hei Hou
The mini-boss of this stage, Hei Hou, wields an axe and chops sections of tree trunks to throw at the player. It is a large forest filled with hills and giant mushrooms.

Jet Mobile
Robotnik will appear after the weather-changing satellite is destroyed. Upon this, he will fly backwards past trees that hold spikes from one end to another, which vary in height while running after the mad scientist. Occasionally, Robotnik will spray a few of the jets in the front of his machine, either one, the other, or both simultaneously. After enough hits, he'll crash into a large tree, with a small tunnel at the bottom which Sonic, Tails, or Knuckles can run through to reach the animal capsule.

Sonic the Fighters
The Zone returns in Sonic the Fighters the area set up on a giant tree stump surrounded by giant mushrooms. In story mode this is the stage in which Espio is fought.

Sonic Jam (Game.com)
Although not explicitly stated, the entire "Sonic & Knuckles" game in Sonic Jam for the Game.com takes place in this zone.

Sonic Generations
Mushroom Hill returns in the 3DS version of Sonic Generations. The level is brought back to life in 2.5 D for both Classic and Modern Sonic (as well with a nice stereoscopic 3-D effect). Classic goes through it in the summer and Modern through the fall.

Archie Comics
In the Archie Sonic continuity, Espio claims this is his native zone. This later turns out to not be the case.

Sonic the Comic
In Sonic the Comic, the entire population of the Emerald Hill Zone was temporarily relocated to the Mushroom Hill Zone (also occasionally referred to as the Mushroom Valley) in order to protect them from Doctor Robotnik.

Trivia

 * On the Sonic the Hedgehog 3 Sound Test (level select) screen, there is an unused level slot called Mushroom Valley. This may have been the original title for this level.
 * The satellite whose destruction restores the state of Mushroom Hill is likely the same environment-changing device mentioned in the Japanese manual of Sonic the Hedgehog 3.
 * In Sonic & Knuckles standalone, there are exactly seven Giant Rings in Mushroom Hill Zone (Act 1 and 2 combined) making it possible to get all emeralds before fighting the boss. In Sonic the Hedgehog 3 & Knuckles, there are eight Giant Rings, due to an added area at the beginning of the level.
 * If the save data is carried over from Sonic the Hedgehog 3, there is a glitch in which some of these Giant Rings will not appear.
 * In Sonic Heroes, Mushroom Hill is mentioned by Knuckles during the stage Frog Forest.