Look Out Below! is the first 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.
This Act has no supporting characters and is played completely in 2D with Modern Sonic. The player is put into a certain section of Green Hill Act 2 that they have to traverse in a set time limit. The main feature of this Act is that many platforms crumble once Sonic steps on them and break apart, forcing the player to make fast and wise decisions when to step on them especially when they are near moving platforms to proceed through the Act. However, if the player fails to do so, there will be Springs that will allow the player to return to higher ground. The platforms will also reappear after a while though it will cost the player some time.