Key Stones are objects that appear in the Sonic the Hedgehog series. They are small figures that can used as keys to open sealed doors or paths by placing them in matching pedestals.
In general, Key Stones are figures that come in sizes ranging from slightly smaller than Sonic's full height to about the size of a head. Each Key Stone have a square rock stand with a figure fixed on top of them, which is usually a lump of crystal, but also sometimes a statuette. All Key Stone types come in different designs and colors. They can be found lying around in specific places in the game's environment.
Key Stones are used to unlock paths and doors blocking the player's path. To unlock such paths with a Key Stone, the player has to grab a Key Stone and take it to a nearby pedestal with colors or symbols matching it and then insert it there by dropping it, which will then unlock the path. If a Key Stone is inserted into a non-matching pedestal, nothing will happen. However, if inserted or just placed in the proximity of its pedestal, the Key Stone will automatically insert itself.
While carrying a Key Stone, a playable character's speed is lowered and their unique actions cannot be performed (e.g. Sonic the Hedgehog's Spin Dash, Tails's Propeller Flight, Sonic the Werehog's Skills etc.).
Sonic Adventure and Sonic Adventure DX: Director's Cut
Key Stones made their first appearance in Sonic Adventure and Sonic Adventure DX: Director's Cut. In these games, the Key Stones are used by the player to open up passages to the Action Stages in the Adventure Fields. Key Stones can be found in the games' Adventure Fields and appear when the player needs it to enter the Action Stage they unlock.
Sonic Adventure and Sonic Adventure DX: Director's Cut feature each a total of four different Key Stones:
|Key Stone||Location||Time of Appearance||Action Stage Unlocked|
|Mystic Ruins, outside Tails' Lab||After Egg Hornet battle||Windy Valley|
|Station Square, Casino area alleyway||After Casinopolis||Icecap|
|Mystic Ruins jungle, near the trolly cart||After Chaos 4 battle||Lost World (w/ other statue)|
|Mystic Ruins jungle, buried ruins with yellow circles indicating it|
In Amy Rose's version of Hot Shelter there are objects called power cubes which works like Key Stones and are used at two points in the Action Stage. When the player inserts a set of four different colored power cubes into their matching fixture, it will unlock new paths.
Sonic Adventure 2
In Sonic Adventure 2 and Sonic Adventure 2: Battle, a variant of the Key Stones called the Gate Key appears in Pyramid Cave. These Key Stones are used to open Gate Key Doors which block obligatory paths through the Stage. One Gate Key is needed for each door which is always located in the nearby vicinity.
Here, the Key Stones are used to solve puzzles inside the Action Stages by finding a certain number of hidden Key Stones and then use them to unlock paths for the player to proceed down. While most doors open and mechanics only need one or two of Key Stones, major doors will need four in total.