Sonic Generations is a platform game in which characters control the titular Sonic the Hedgehog in two forms: Classic and Modern, in which they must collect the seven Chaos Emeralds, free their friends and stop a mysterious entity from creating time holes. The game features levels derived from 20 years of Sonic history, spreading across three eras, each having three stages and two bosses from previous games: Classic, Dreamcast and Modern, which are played as either Classic Sonic or Modern Sonic. Classic Sonic's levels are strictly two dimensional side scrolling stages, using classic moves like the Spin Attack and Spin Dash, while Modern Sonic's levels follow the 2D/3D style gameplay of Sonic Unleashed and Sonic Colors, featuring techniques such as boosting and homing attacks. As well as classic power-ups such as Invincibility and Speed Shoes, certain levels have unique power-ups, such as skateboards in City Escape and Wisp powers in Planet Wisp. Classic and Modern Sonic begin the game with six lives, which are lost when they suffer any type of damage with no rings in their possession, or fall into a pit. More lives can be earned by getting 100 rings or finding a symbol to collect their lives. If the player runs out of lives, the game is over. However, the game can be continued by selecting "Yes" at the "Try Again" screen.