Boss Gate Keys

Boss Gate Keys or Boss Keys are special keys that appeared in Sonic Unleashed and Sonic Generations. These keys are needed in order to gain access to the level's boss and to progress further in the game.

In Sonic Unleashed
The first Boss Keys appeared on the PS3/Xbox360 version of Sonic Unleashed under the name of Gaia Keys(ガイア神殿の鍵 Gaia shinden no kagi?, lit. "Key to the Gaia temple"). These keys were created in ancient times to unlock certain Gaia Gates (called the Boss Gate by Professor Pickle). After it is unlocked, these Gaia Gates give access to the area of the local Temple of Gaia, which is guarded by the level's boss that Sonic must defeat to enter. Each Gaia Key for each temple is split into halves; one daytime half and one nighttime half. Sonic must collect the corresponding halves from each respective continent to form one Gaia Key. In the story, Sonic does not need a Gaia Gate to locate the temple in Eggmanland, Mazuri, and Chun-nan due to one being located near the Goal Ring in the first while the other two is by predetermined events.

In Sonic Generations
In the console/PC version of Sonic Generations, the Boss Keys are needed to open the Boss Gates found in White Space. Each Boss Gate found in the White Space requires three Boss Gate Keys in order to be unlocked; adding to the total of nine found in the game. After both Classic Sonic and Modern Sonic restore the colors of all three levels found in an area of White Space, three Boss Gate Keys will appear in that area, but surrounded by an inaccessible barrier. To obtain the keys, the Sonics must clear one Challenge Act Gate for each of the Boss Gate Keys found in their respective area. After it is cleared, their barriers will be lowered and the keys will be available to be collected. These keys will unlock the bosses Death Egg Robot, Perfect Chaos, and Egg Dragoon.