Challenge Act Gate

The Challenge Act Gates are portals that appear in Sonic Generations. After Modern Sonic and Classic Sonic restores the colors and space for every three sets of levels in the White Space, the Challenge Act Gates will appear in the area surrounding them.

Upon entering them, the Sonics can play a specific mission, and once that mission has been cleared, a golden bell, called a Bonus Bell will appear on top of the Challenge Act Gate. When these bells are rung, they will release a floating note that contains one of the game's collectables, concerning music and Artwork. These notes however, has to be caught within 20 seconds or they will fade away.

Just as the Sonics can restore color to a level by the acts, the Sonic can restore more color to the White Space by clearing the Challenge Act Gates. For every fifth Challenge Act Gate the Sonics clear, a part of the color in the White Space will be restored.

The Challenge Act Gate appearance variates for Classic and Modern Sonic; For Modern Sonic, the Challenge Act Gates will have the curve at the top and the flat end at the bottom, while for Classic Sonic this order will be reversed.

Type of Challenges Act Gates
Each Challenge Act Gate contains a mission of a certain type, which is marked by an icon on top of the Challenge Act Gate. These types are as following:
 * Speed: - The Sonics have to race through an obstacles courses within a certain time limit.
 * Techniqe: - Serving as more technical missions, the Sonics have to utilze skills and tactics to pass the mission as fast a possible.
 * Doppelganger: - The Sonics have to race against a Sonic copy throughout the levels and reach the goal first.
 * Friends: - The Sonics have to team up with their friends to clear the mission, or compete, and win, against them.
 * Enemy: - The enemies has been tweaked to make them more challenging (such as increasing their speed or number) and the Sonics have to pass through them and reach the goal.
 * Item: - The Sonics (mostly Classic Sonic) have to use Item boxes in order to clear the mission and reach the goal.
 * Ring: - The Sonics have to clear missions regarding rings, such as to pass through an act with only one ring or collect a set amount of rings and reach the goal.
 * Juggle: - Classic Sonic has to bring the Goal Plate to the end of the level, without dropping it.
 * Rescue: - Classic Sonic has to free a certain amount of Animal friends and reach the goal before runing out of time.