The Boss Gate is a recurring object in the Sonic the Hedgehog series. As their name suggest, these gates grant access to their respective game's bosses.
Boss Gates are portals of varying designs that can be found in the hub worlds of their respective games. By using or entering these portals in gameplay, the player will initiate a battle with one of the game's bosses. Because defeating a boss is needed to progress with the game, the Boss Gates are always obligatory to use at one point.
Multiple Boss Gates can be found within each game. Each boss in such Sonic games will have their own Boss Gate. However, in order to use a Boss Gate, the player must first fulfill certain requirements. This can be finding the Boss Gate Key(s) that will unlock the Boss Gate, or clearing a certain amount of levels.
In this game, the Boss Gates are circular pads with a red light emerging from them which displays the symbol typically associated with Dark Gaia. They are named "Boss Gates" by Professor Pickle due to the strong opponents that lurk behind them.
Boss Gates can typically be found in the Entrance Stages. The only exceptions are Eggmanland's Boss Gates, which are located in the Eggmanland Town Stage. To unlock a Boss Gate in most cases, the player has to obtain the Boss Gate's associated Gaia Key. Other Boss Gates are unlocked after the player clears a specific Act.
In the PlayStation 2/Nintendo Wii version of Sonic Unleashed, Boss Gates are not featured; instead, there is a door with star patterns on it inside each Gaia Gate that leads to the Boss Stage. The player can unlock these doors by assembling the matching Planet Tablet from the fragments collected in the Stages.
In this game, the Boss Gates are floating portal made of gears, cogs, and locks. However, the Interior of the Boss Gates are much more elaborate, each featuring a large black and white hallway with white chandeliers and a wall with transparent glass cutting through the middle of said hallway. At each end of each hallway is a stone door that respectively leads to the boss and back to White Space.
In the console/PC version of Sonic Generations, the Boss Gates are located in the White Space hub world; they can be found at the right of each of White Space's three Areas. To enter a Boss Gate, the player needs to have acquired all three Boss Gate Keys for it. After getting all three keys, the player only needs to approach the Boss Gate and enter it as it was a regular Stage. After clearing a Boss Gate, a Chaos Emerald is restored from its colorless state and passed on to the player.
In the Nintendo 3DS version, the Boss Gates have both a rival and a big opponent (Metal Sonic and Big Arm in the first one, Shadow and the Biolizard in the second one, and Silver and the Egg Emperor in the third one). In order to open the gates, the player must restore all of the stage of each era. Once they reach a Boss Gate, they must defeat the rival in a race before they can battle the major opponent.
↑Sonic Team (9 December 2008). Sonic Unleashed. PlayStation 3. Sega. Area/Level: Collection Room. "Prof. Pickle: You'll use large devices like the Gaia Gates to access each temple. They'll likely be guarded by Eggman's best and brightest, so be ready. Because of the threats lurking behind them, I call these Boss Gates. You'll need to acquire a special Boss Key in order to activate each gate."