Sonic Adventure 3: Returning of Energy

Sonic the Hedgehog
Abilities: Homing Attack, Spin Dash, Infinite Spin Dash (Warning: Difficult to steer with infinite spin dash)

Gameplay: Platforming (focused on running)

Miles "Tails" Prower
Abilities: Spin Dash, Tail Whip, Temporary Flight

Gameplay: Platforming (evenly focused on running and flight skills)

Knuckles the Echidna
Abilities: Spin Dash, Glide, Climb, Digging Attack, Punch Combos

Gameplay: Beat em' Up/Platforming

Shadow the Hedgehog
Abilities: Spin Dash, Homing Attack, Guns, Vehicles

Gameplay: Platforming (focused on alternate ways to get to the goal)

Blaze the Cat
Abilities: Spin Dash, Temporary Hover, Tricks, Boost

Gameplay: Platforming (Sonic Rush style in 3D)

Metal Sonic
Abilities: Spin Dash, Homing Attack, Double Jump

Gameplay: Platforming (Sonic style, more difficult level design and enemy placement)

Side Characters
Amy Rose

Vector the Croccodile

Espio the Chamelion

Silver the Hedgehog

Cream the Rabbit

Cheese the Chao

Mecha Sonic

E-Series Robots

Badniks

Egg Pawns

Heavy and Bomb (Referenced)

South Island

 * Green Resort (Sonic, Tails, Knuckles)
 * Rocky Canyon (Sonic, Tails, Blaze)
 * Marble Cavern (Knuckles, Blaze, Metal Sonic)
 * Casino Hall (Sonic, Tails, Metal Sonic)
 * Mechanical Yard (Sonic, Knuckles, Shadow)
 * New Stardust Speedway (Sonic, Shadow, Metal Sonic)

Station Square

 * Rapid Highway (Sonic, Tails, Metal Sonic)
 * Twilight Park (Sonic, Tails, Blaze)
 * Jet Set Railway (Sonic, Shadow, Blaze, Metal Sonic)
 * Silent Street (Knuckles, Shadow, Blaze)
 * Desert Drive (Shadow, Blaze, Metal Sonic)

Mystic Ruins

 * Windy Hilltop (Tails, Knuckles, Blaze)
 * Ice Capital (Sonic, Tails, Knuckles)
 * Hidden Workbench (Sonic, Tails, Metal Sonic)
 * Lost World Underground (Knuckles, Shadow, Blaze)
 * Crimson Volcano (Sonic, Shadow, Blaze)
 * Egg Country (Sonic, Tails, Metal Sonic)

Sky Islands

 * Angel Island (Sonic, Tails, Knuckles)
 * Sky Babylon (Tails, Shadow, Blaze)
 * Sky Soldiers (Sonic, Shadow, Metal Sonic)
 * Hydrocity Highway (Sonic, Tails, Blaze)
 * Isle Eggman (Sonic, Tails, Knuckles, Metal Sonic)

Egg Genesis

 * Egg Armory (Shadow, Blaze, Metal Sonic)
 * Inner Genesis (Sonic, Tails, Knuckles)
 * Egg Generation (Sonic, Tails, Knuckles, Shadow, Blaze, Metal Sonic)

Other
Sonic the Hedgehog
 * Flight to Sky Islands (Sonic and Tails, Knuckles and Shadow and Blaze)
 * Flight to Egg Genesis (Sonic and Knuckles, Tails and Blaze, Shadow and Metal Sonic)
 * Shooting Range (Shadow)
 * Dojo (Knuckles)
 * Grind Square (Blaze)
 * Ice Cap Snowboarding (Sonic, Tails, Metal Sonic)
 * Chao Garden (Sonic, Tails, Knuckles, Shadow, Blaze, Metal Sonic)
 * Casinopolis Pinball Party (Sonic, Tails, Knuckles, Shadow, Blaze, Metal Sonic)

NIGHTS Into Dreams

Jet Set Radio

Knuckles' Chaotix

Toxic Caves

Almighty Palace
Sonic - Collect Blue Spheres, Avoid Hazards, Don't Fall or Lose Rings

Tails - Collect Orange Spheres with Tornado, Dodge Badniks and Don't Lose Rings

Knuckles - Convert Red Spheres into Blue Spheres Sonic 3 & Knuckles Style (Avoid Blue Spheres, Speed will increase as stage goes on)

Shadow - Shoot all of the Enemies with provided ammo. (No Additional Ammo; Don't run out!)

Blaze - Grind through entire stage; Avoid enemies, don't fall

Metal Sonic - Fly with Rocket Metal and Boost to Destroy Blue, Orange, and Red Spheres. Don't lose rings, avoid Tails RCs.

Collect for Super Form
7 Chaos Emeralds - Sonic, Knuckles, Shadow, Metal Sonic

7 Super Emeralds - Tails

7 Sol Emeralds - Blaze

Sonic

 * Lightspeed Shoes - Run along a trail of rings
 * Foot Gel - Gives Sonic Bounce Ability
 * Chaos Ring - Increases Bounce Speed
 * Lightspeed Light Attack - Gives Lightspeed Attack
 * Magic Hands - Decreases ring spread when hit.

Tails

 * Jet Anklet - Increases Flight Speed
 * Blue Ribbon - Infinite tail whip
 * Chaos Ring - Increases flight stamina
 * Wrist Radar - Increases flight accuracy

Knuckles

 * Level-Up System - Bank your rings and purchase additional punch combos

Shadow

 * Lightspeed Skates - Run along a trail of rings
 * Foot Gel - Gives Shadow bounce ability
 * Chaos Ring - Gives Shadow Chaos Spear
 * Mind of Shadow - Gives Shadow Fever

Blaze

 * Chaos Ring - Increases Trick Speed
 * Flame Heels - Increases hover use
 * Flame Band - Decreases Boost depletion

Metal Sonic

 * Lightspeed Data - Run along a trail of rings
 * Lightspeed Attack Data - Gives Lightspeed Attack
 * Bounce Data - Gives Metal Sonic bounce ability
 * Ring Data - Decreases Ring Spread when hit
 * Chaos Data - Gives Metal Sonic Fever

Super Forms
Super Sonic - Increases jump height and run speed

Super Tails - Increases run speed, flight speed, calls upon 4 Flickies to assist in defeating enemies

Super Knuckles - Increases run speed, climb speed, glide speed, and punch speed

Super Shadow - Increases jump height, run speed, unlimited ammo

Burning Blaze - Increases jump speed, run speed, boost speed, and trick speed.

Super Metal Sonic - Increases jump height and run speed

(Beware of the ring consumption for all)

Bosses

 * Egg Eagle (Sonic, Tails, Knuckles)
 * Knuckles (Sonic, Tails, Shadow, Metal Sonic)
 * Egg Serprent (Shadow, Blaze)
 * Grand RC (Metal Sonic)
 * Shadow (Tails, Blaze)
 * Blaze Race (Sonic, Shadow)
 * Egg Turtloid (Sonic, Knuckles)
 * Egg Armageddon (Shadow)
 * Tails (Shadow, Knuckles)
 * Sonic Race (Blaze, Metal Sonic)
 * Metal Sonic Race (Sonic)
 * Metal Sonic (Knuckles)
 * Flying Battery Fort (Sonic, Tails)
 * Egg Lancer MK II (Blaze)
 * Egg Zeppelin (Shadow)
 * Egg Emperor MK III (Sonic, Metal Sonic)
 * Mecha Sonic (Sonic, Tails, Knuckles, Metal Sonic)
 * Super Mecha Sonic (Metal Sonic)
 * E-9000 (Shadow, Metal Sonic)
 * Egg Station (Shadow, Blaze)
 * Egg Powerhouse (Knuckles)
 * Egg Domination (Sonic, Tails, Knuckles, Shadow, Blaze, Metal Sonic)
 * Egg Genesis Mech (Super Sonic)

Story
Sonic and Tails - Just chilling at home in South Island, Sonic later gets called from Tails saying that Eggman has returned, but this time he has simply gone on a robot ambush. They head over to Station Square and the Mystic Ruins to clear out the problem. Realizing this is more difficult, Sonic and Tails realize that Eggman has also flooded South Island with his robots. Sonic and Tails venture back and forth through locations, also meeting up with some old friends and rivals. They see that Eggman has really thought this dominoes plan out.

Knuckles - On Angel Island, one day Knuckles realized that he has sensed a strange depletion of energy from Angel Island, as well as the neighboring islands. Heading down to meet Sonic and Tails, he sees the world below is over-run by Eggman robots, Knuckles hurries to find allies, and destroys any robot that gets in his way.

Shadow and Blaze - Also concerned about the massive increase in Eggman robots, Shadow heads to destroy them and Eggman alone. Although Sonic, Tails, and Knuckles get in his way, he also partners up with Blaze the Cat, trusting her because of her serious attitude towards the situation.

Metal Sonic - Returning as Eggman's robotic equal to Sonic, Metal Sonic, along with Mecha Sonic and other robots are here to make sure Sonic and friends don't get in the way. Metal Sonic later finds to believe himself as more powerful than Eggman and betrays him, plotting to overthrow him. Eggman later finds out that Metal Sonic has been destroying his mechs, and he turns all of them, including Mecha Sonic against Metal Sonic. Metal Sonic then teams up with Sonic and friends, with the intention of betraying them once Eggman has been defeated.

Eggman - From his last defeat, he has been hidden away for a while. A LONG while. Eggman has returned once again with his largest army and largest airship yet, the Egg Genesis. Using special weaponry the Egg Genesis harnesses power from powerful sources such as the Master Emerald without having to steal any objects. His intentions are as before: conquer the world and create the Eggman Empire.