Adventure through the mystical Northstar Islands in this all-new take on classic 2D Sonic high-speed action platforming. Play as Sonic, Tails, Knuckles, and Amy and harness all-new Emerald powers to move and attack in dynamic new ways. Navigate gorgeous, never-before-seen environments solo or with up to 3 other players and stop Dr. Eggman, Fang, and a mysterious new adversary from converting the islands’ giant animals into Badniks before it’s too late!

• A new Spin on a Classic: The 2D Sonic high-speed sidescrolling action platforming you know and love, reimagined with fully 3D graphics, new powers and abilities, an all-new setting, and new ways to play! You’ve never played classic Sonic like this before!
• Play as your Favorite Characters: Choose from Sonic, Tails, Knuckles, and Amy and take advantage of their unique abilities to blaze a path across the Northstar Islands as they race to defeat Dr. Eggman, who has teamed up with an old nemesis, Fang, and a mysterious new armored adversary.
• Harness the Power of the Chaos Emeralds: Multiply, swim up waterfalls, change form, and more with the powers of the Chaos Emeralds.
• More Friends, More Fun: For the first time ever in a Sonic game, play through the entire campaign with up to 3 other players with drop-in and drop-out 4-Player Local Co-op.
• Challenge Players From Around the World: Compete locally or online with up to 8 players in the all-new Battle Mode!

To activate the game, you need a Steam Account

• Login or register at the official
  Steam Website and download Steam client
• Install and start application, login with your Account name and Password
• Click the Games Menu.
• Choose Activate a Product on Steam...
• Follow the onscreen instructions to complete the process
• After the successful code verification, go to the "MY GAMES" tab and start downloading.