unlocked upon completing the first three. Sonic's story focuses on the speed-based platforming seen in previous Sonic games, with some sections having him run at full speed while dodging obstacles or riding a snowboard. Another character, Princess Elise, must be escorted in some stages, and she can use a special barrier to guard Sonic. Shadow's sections are similarly speedy, albeit more combat-oriented, with some segments having him ride vehicles. In contrast, Silver's levels are slower and revolve around his use of telekinesis to defeat enemies and solve puzzles. In certain areas, control is switched to one of several friend characters, with their own abilities. Although each character traverses the same levels, their unique abilities allow the player to access different areas of each stage and prevent them from accessing certain items. Scattered through each level are golden rings, which serve as a form of health. The rings can protect a character from a single hit by an enemy or obstacle, at which point they will be scattered and blink before disappearing. The game begins with Sonic, Shadow, and Silver each assigned a limited number of lives. These lives are successively lost whenever, with no rings in their possession, the characters are hit by an enemy or obstacle or encounter other fatal hazards. The game ends when the player exhausts the characters' lives. Every few levels, players will encounter a boss stage; to proceed, they must defeat the boss by depleting its health meter. Upon completion of a level or mission, players are given a grade depending on their performance, with an "S" rank being the best and a "D" rank being the worst. Players are given money for completing missions; more money is given to higher ranks. This money can be used to buy upgrades for the player character. Certain upgrades are required to complete the game. The game also features two multiplayer modes: "Tag", a cooperative mode where two players must work together to clear levels and collect Chaos Emeralds, and "Battle", a player versus player mode where two players race against each other. Plot Doctor Eggman kidnaps Princess Elise of Soleanna in the hopes of harnessing the Flames of Disaster, a destructive power sealed within her. Aided by his friends Tails and Knuckles, Sonic works to protect Elise from Eggman. Meanwhile, Shadow, his fellow agent Rouge, and Eggman accidentally release an evil spirit, Mephiles. The spirit transports the