Complete the following storylines to obtain the following characters.
Amigo: Complete all missions.
Billy: Complete all missions.
Blaze: Complete Babylon Story.
Cream The Rabbit: Complete Hero Story.
Eggman: Complete Babylon Story.
NiGHTS: Complete all missions.
Rouge The Bat: Complete Hero Story.
SCR-GP: Complete Babylon Story.
Shadow The Hedgehog: Complete Hero Story.
Silver: Complete Babylon Story.
Bonuses
Complete the indicated task to unlock the corresponding bonus.
80s Boulevard: Complete Babylon Story.
90s Boulevard: Complete Babylon Story.
World Grand Prix mode: Complete Hero Story.
Crimson Tower: Shortcut
When in the crimson crater, get to the vertical wall where you go down to the speed mats and get the boost up. Instead, use gravity. As soon as you jump, hold Square and point up. Let go and you will fly and grip onto the track.
Easy rings
Enter Mission mode and select Mission 2, "Collect 'X' Rings" on any of the tracks. During this mission you are not limited to a set number of rings that you can collect. Collect as many rings as possible before reaching the goal, then wait for the results screen to appear. Once the results finish displaying, all the rings you have collected will be automatically sent to your ring account (although the game will not show you this). Pause game play and select "Restart" to begin the mission again. Keep repeating the process. If you can get at least 250 rings per try, you should have collected enough rings to purchase even the Rainbow gear within an hour or two.
The Gambler gear at the shop has an interesting secret. If you have bought it and take it on a World Grand Prix, you can earn 500 rings per race. If you finish in first place in the Grand Prix on top of that, you will get a total of 3,500 rings. Just three Grand Prixes will give you enough rings to buy the rainbow in exactly one hour. Note: You must know your courses well though, because the Gambler cannot take type shortcuts.
Enter the Grand Prix with a partner. Finish in first place three times, then second place three times each. You should finish equal in first and receive 500 rings each.
Extra character!
After getting your playtime up to 140 hours you unlock SCR-HD which is the equivalent to SCR-GP, but this new SCR-HD can fly but he can NOT knock down baracades.
Gear
Complete the indicated task to unlock the corresponding gear.
Chaos Emerald gear: Earn an "Extreme" rank on all missions in Story mode.
MAG gear: Complete all missions in Story mode.
Mission mode
Successfully complete Babylon Story or Hero Story. When that storyline is played again, you can choose any stage and play in Mission mode.
Mobius Strip: Easy hits
Choose any character that can use a flying gear or, just use the Angel - Devil gear if available. On the second long strip that has the flying ramp, make sure you are able to fly by this point. Go up the ramp, fly, and hold it as long as possible. Do not fly too high or too low. This slows down the Zero Gravity trigger so when your gear hits the ground you will zoom to the Boss for a speedy hit. This is useful after several hits when the time to attack shortens.
Movies
Complete the indicated task to unlock the corresponding movie.
Bonus characters...