- You may be looking for a different Challenge Act, 200% Boost Gauge Challenge.
300% Boost Gauge Challenge is the fifth and final Challenge Act of Green Hill Act 2 in the console/PC version of Sonic Generations. It is unlocked after clearing every Stage in the classic era and is playable only as Modern Sonic.
In this Challenge Act, Modern Sonic must run through Green Hill Act 2 as fast as he can; this time his tripled Boost Gauge capacity will help him along the way. The level starts with large sections of 2D platforming, in which the Homing Attack can be quite useful, but near the end Sonic enters a 3D section. Regardless of the camera angle, the player must use the Boost to his/her advantage with precise timing to reach the Goal as quickly as possible. To acquire an S-rank, the player must reach the Goal Ring in one minute ten seconds (1:10). Once this Challenge Act is completed, the "Boost Gauge Up" Skill will become available in the Skill Shop.