Unlock new Extreme Gear
Beating the game's modes yields new goodies for use by most or all characters:

Blue Star II (Sonic's board) - Beat the Babel Story
Darkness (Shadow's jet sneakers) - Beat the Hero Story
Egg-Rider (Eggman's scooter) - Beat the Babel Story
Magic Carpet - Beat the Babel Story

Bonus characters
Successfully complete the Hero storyline to unlock Shadow The Hedgehog, Rouge The Bat, and Cream The Rabbit.

Successfully complete the Babylon storyline to unlock Eggman.

Bonus vehicles
Successfully complete the Hero storyline to unlock Shadow's Darkness jet shoes, Rouge's Temptation board, and Cream's Smile board.

Successfully complete the Babylon storyline to unlock Sonic's Blue Star II board, Eggman's Egg-Rider scooter, and the Magic Carpet.

Bonus modes
Successfully complete the Hero storyline to unlock Mission mode, Babylon storyline, and the ability to buy skates at the shop.

Automated trails
To use automated trails to your advantage, wait for when the Analog-stick spinning part begins. When you spin it, it fills your air gauge. However if you keep spinning it beyond that, the speed meter will go faster up to a certain point.

Turbulence
To use turbulence effectively, wait for it to appear and ride on it. After you see arrows on the side, move towards it to gain speed and air. Also, it is an effective way to get in position to pass and hit an opponent.

Defeating Babylonian God
To defeat this giant, play as Sonic. He has three lives. To catch him, get a good head start. He is very quick. Do not make a mistake or it will take awhile to catch up. When you start, you must catch up to him using the turbulence streams and the grind rails. It helps to make quick work of him. Also, use the ramps and try to make the most tricks you can, but do not take any unnecessary risks. After you start getting close to him, use your boost to go through the lamp-like object below him, and he will let out a cry. Then the stage will look like a digital place for a period of time. After it returns to normal, repeat the process. After the third strike you deliver, it will quickly turn into a race. If you are near the finish line, use the turbulence and your boosts at any costs. When you win you will see an intermission sequence showing what the legendary treasure really is.

Egg Factory: Avoid losing speed
Instead of losing speed when hitting the lava, boost through it to keep your velocity.

Faster boosts and stronger attacks
Depending on what level your attacks are, they will last for a longer time and have a paralyzing effect. At level 1, you will have a short boost and weak attacks; and no paralyzing. At level 2, you will have a medium sized boost and stronger impact on enemies; and short Paralysis. At level 3, you will have the longest sized boost and a powerful paralyzing attack on your enemies.

Splash Canyon: Shortcut
As Tails in level 2 of the Hero storyline, there is a shortcut in a waterfall. After you make the first jump, when you are turning around the bend there is a waterfall. If you go through the beginning of it, you will find a fly kicker and accelerators.

Faster boosts and stronger attacks
Depending on what level your attacks are, they will last for a longer time and have a paralyzing effect. At level 1, you will have a short boost and weak attacks; and no paralyzing. At level 2, you will have a medium sized boost and stronger impact on enemies; and short Paralysis. At level 3, you will have the longest sized boost and a powerful paralyzing attack on your enemies.

Automated trails
To use automated trails to your advantage, wait for when the Analog-stick spinning part begins. When you spin it, it fills your air gauge. However if you keep spinning it beyond that, the speed meter will go faster up to a certain point.

Trick set
Every character has three sets of tricks that can be done. To see all three sets you must use the skates, boards, and motorcycles.

Voice announcer
When you play as Shadow, first perform a few tricks. If you listen closely, you can hear the announcer say "She has made a perfect landing!" or "She landed perfectly and has taken advantage of the speed boost."

New Gear in the Shop
To unlock new, exclusive gear in the shop, perform the following tasks:

"Super Hang-On" Gear
Complete all of Jet, Wave and Storm's Missions

"Hang-On" Gear
Complete all of Jet, Wave and Storm's Missions

"The Crazy" Gear
Complete all of Jet, Wave and Storm's Missions

"Opa Opa" Gear
Complete all of Jet, Wave and Storm's Missions

Audio Room BGM
To unlock game tracks in the Audio Room under the Extras menu, perform the following tasks:

"Catch Me If You Can"
Complete Babylon Story in Story Mode

"Theme of SEGA Carnival"
Unlock the SEGA Carnival Track in World Grand Prix

"Theme of Babylon Garden"
Complete Heroes Story in Story Mode

"Theme of Digital Dimension"
Complete Babylon Story in Story Mode

Hidden Tracks
SEGA Carnival - Beat Heroes Cup w/ Gold Emblem
SEGA Illusion - Beat Babylon Cup w/ Gold Emblem

Hidden Cameo Characters
AiAi - Beat all Jet, Wave and Storm missions
Nights - Beat all Jet, Wave and Storm missions
Ulala - Beat all Jet, Wave and Storm missions

Unlocking Boards/Scooters/Sneakers
Blue Star II (Sonic's Board) - Beat Babylon Story
Darkness (Shadow's Sneakers) - Beat Hero Story
Egg-Rider (Eggman's Scooter) - Beat Babylon Story
Magic Carpet - Beat Babylon Story
Skate type (Shadow's Sneakers) - Beat Hero Story
Bike type (Different Styles of Boards/Scooters) - Beat Babylon Story

New Characters
To unlock new playable characters, perform the following tasks:

E-10000G - Play for 20 hours straight.
Dr. Eggman - Complete Babylon Story
Rouge The Bat - Complete Hero Story
Shadow The Hedgehog - Complete Hero Story
Cream The Rabbit - Complete Hero Story
Super Sonic - Complete all Missions in Mission Mode with a Gold Emblem
E-10000R - Play the game for at least 50 hours

New Story Mode
To unlock the new Story Mode, perform the following task:Babylon Story Complete Hero Story

Unlock Super Powers
Beat everyone with super Sonic in "Free Race" to unlock everones' full power. Shadow will be Super Shadow, Knuckles will be hyper Knuckles, and Tails will be Turbo Tails and (surprisingly) Eggman will be buff. (What are the ods...)
Also everyone will have infinate air tanks.