Green Hill is the first stage in Sonic Generations for the PC, PS3, and Xbox 360. Classic and Modern Sonic revisit the original chequered fields of Green Hill Zone from Sonic the Hedgehog. Act 1 starts as a scrupulously faithful remake of the Mega Drive level, right down to the positioning of platforms and hidden springs, but variety is soon introduced (with the helical strips from Emerald Hill Zone, for example). In Act 2, meanwhile, modern Sonic faces a thoroughly updated version, with Quick Step routes, grindrails, and dash panels.
Green Hill is the only stage in both the console and handheld versions of the game, and unlike its handheld counterpart Classic Sonic has a completely new layout for his act. As well as being the first zone to be announced, it is the only playable level within both Sonic Generations demos.
The game opens straight into Act 1, where Classic Sonic is enjoying a jog through the tropical zone. He notices the Time Eater which unleashes a spell over his world. Fast forward into the present, and Modern Sonic gets his birthday party rather rudely trashed by Time Eater, and is cast into a strange white void. The bleached entrance to Green Hill Act 2 is in front of Sonic when he wakes up, and after speeding through the stage, a frozen Tails is returned to life. The fox mentions that, unlike Sonic, he doesn't remember having been here before - a reference to his absence from Sonic the Hedgehog.
- Chopper — Leap out from under log bridges as in the original. However, now they spend some of their time in the background, so can't always be hit. Found only in Act 1.
- Mega Chopper - Supersized version of the original, with a taste for underground grindrails.
- Buzzbomber — Flying hornet-bots that scroll through the air firing shots at you. As well as the standard versions, Generations introduces purple buzzbombers which just hover to serve as homing attack fodder. Also, one of the Green Hill missions is to race Knuckles through a stage filled with motionless giant badniks, of which a giant purple buzzbomber is one variety.
- Motobug - A mechanised ladybird which remains the scourge of slow-moving, non-jumping hedgehogs. In 2D, they'll make a dash towards Sonic if he's spotted, but they're completely static in 3D. Has a giant version in the Knuckles mission.
- Crabmeat - Now fires missiles instead of energy balls, but otherwise behaves as always. Laughs at Sonic if he is damaged by it.