High Speed Hijinks is the fourth Challenge Act of Seaside Hill Act 1 in the console/PC version of Sonic Generations. It is unlocked after clearing every Stage in the Dreamcast era and is playable only as Classic Sonic.
The player takes control of Classic Sonic in Seaside Hill Act 1 with no supporting characters. As the name would imply, during this Challenge Act, everything, excluding Sonic himself, move at double their normal speed. The increase in speed is meant to make it harder for the player to navigate through the given area to the goal. This includes enemies such as the Egg Pawns and the bullets they shoot, as well as moving platforms.