Doppelganger Race!

"Face off against Sonic's double and beat him in a race to the goal."

- Description

A doppelganger race is a type of Challenge Act featured in Sonic Generations. It is marked on the Challenge Act Gate with a gray version of the Extra Life symbol.

Guide
In this Challenge Act, Sonic must race against a faint version of himself, the "doppelganger", in an exact copy the specified level. The doppelganger seems to be in his own version of the level, as when the player destroys an enemy before the doppelganger, the doppelganger jumps on an invisible enemy in that exact location, no matter how much time has passed. There are no advantages given to either Sonic or the doppelganger, so that the player cannot use unfair advantages to win or complain that the mission is too difficult to pass. In order to complete the mission, Sonic must simply reach the Goal before the doppelganger does.

Trivia

 * This is the only Challenge Act to be playable for every level in the game, Classic and Modern.
 * This is the only Challenge Act to be an exact copy of the stage it is based upon.