Knuckles' Chaotix was the first Sonic game with a large playable cast of characters. It is also one of the few games in the series where Sonic isn't playable at all, though oddly enough Metal Sonic makes an appearance.
The Chaotix are Knuckles' group of fighters. They don't reappear for almost 9 years until Sonic Heroes.
Knuckles is the leader of the Chaotix and Guardian of Angel Island and the Master Emerald. This is Knuckles' first solo venture. Knuckles is out to stop Eggman and protect the Carnival Island. He retains his Climbing and Gliding abilities from Sonic & Knuckles.
- The games starts out with Knuckles alone, until he finds Eggman busy imprisoning Espio.
Espio the Chameleon
Espio is the first member of the Chaotix that Knuckles runs into and frees from Eggman and Metal Sonic's robotic claws. Espio follows a ninja-like discipline and has a tornado move that acts similar to Spin Dash. He has the ability to walk up walls, and even onto ceilings. Espio, unlike the majority of the Sonic characters, is very serious, calm and disciplined. He is talented with computers, and plays the shamisen, a stringed instrument, as a hobby. According to the Japanese Chaotix game manual, Espio especially dislikes Dr. Eggman, although it's not stated precisely why.
Vector the Crocodile
In Knuckles' absence, Vector often acts as the leader of the Chaotix. Vector and Espio are the only reptilian characters in the Sonic universe. Vector is known to do just about anything for money, as long as it's legal. He has a somewhat rough and rude personality, but deep down he's actually quite a kind soul, and has been known to occasionally help people for charity. Although his brash attitude and childish behavior might make him appear otherwise, Vector is in fact a very clever and capable leader. Besides money, Vector's main joys in life are music, food and sports drinks.
- Vector is one of the oldest Sonic characters; He was originally designed to appear in Sonic's band in Sonic the Hedgehog 1's Sound Test.
Charmy the Bee
Charmy is one of the youngest characters in the Sonic series. According to the Japanese manual, Charmy is out doing what bees do best when he arrives at an island and is captured by Doctor Eggman, who is currently taking over the island. In the US version, he is a friend of Knuckles the Echidna who is visiting "Carnival Island" when Eggman makes a surprise attack on the island.In both cases, he is captured and placed in Eggman's "Combi-Confiner", and becomes one of the several characters the player can choose to play as, or play with (as a partner character). Charmy can fly, and can as such do a dash in any direction instead of jumping. He can also start hover, which allows him and his partner to fall at a much slower and controlled rate. Charmy is hyperactive, scatter brained, and not too bright. Being a child, he would rather play than work. Due to his age, he is not as skilled a detective as Vector or Espio, but he is nonetheless valuable to the team. He is also the most friendly and optimistic of all Chaotix members.
Mighty the Armadillo
Mighty is also one of the oldest Sonic characters, perhaps even older than Sonic himself. Mighty's design is actually an early look for Sonic, and many of his sprites in this game resemble those used by Sonic in the prototype game, Sonic Crackers. Unlike the rest of the Chaotix, this isn't Mighty's first appearance. He, along with Sonic and Ray the Flying Squirrel, were captured by Eggman and had to break out in an Arcade game called SegaSonic Arcade. According to the Japanese manual, he just happened to stumble across the island which the adventure is set on during his explorations. The American manual states that he is a friend of Knuckles the Echidna and happens to visit "Carnival Island" when Eggman attacks. Mighty, like most members of the Chaotix, has the ability to climb walls by jumping off and back.
- Mighty is a gentle and caring pacifist, only using his strength and fighting abilities when there is no other option. He loves to travel, and his dream is to journey to all places of the world. According to the Japanese booklet of Chaotix, Mighty enjoys forest bathing, likes peace and nature, and detests violence.
Heavy and Bomb
Heavy and Bomb are two of Eggman's Robots who managed to escape and pledge to aid the Chaotix for revenge. It is unknown if this story is true, however; Heavy and Bomb are fairly useless, and after Eggman is defeated they are never seen again. Some speculate that they may have been sent by Eggman in an attempt to slow the Chaotix down. Heavy was Eggman's chief mechanic. Heavy has an impenetrable outer skin, and can destroy enemies when touched, can't be hurt by spikes, but is so heavy that he slows down his partner considerably. Bomb is an explosive animated bomb, and when he comes in contact with an enemy, he explodes. He regenerates almost instantly, but poses a threat to ally and enemy alike.
- Heavy and Bomb are usually regarded as booby prizes, for people who aren't fast enough choosing their partner from the combi-confiner. They also appear twice in the character select, which led some to believe that they were last minute replacements for Sonic and Tails.
As usual, Eggman is the enemy trying to take over the world, or in this case, more specifically Carnival Island. Eggman wants the Chaos Rings all to himself, and also seeks to steal the power source for the whole island, the Master Emerald. His primary tool for this is Metal Sonic. Eggman captured the Chaotix and ran them through the Combi-Confiner, forcing them to be stuck together in pairs.
Metal Sonic makes his first reappearance since Sonic CD in this game. Metal Sonic is the main enemy and, after a transformation, becomes the Super Metal Sonic, serving as the final boss.
Amy makes a cameo in the game's Sound test.
Sonic & Tails
Sonic & Tails, aboard the biplane Tornado, show up in the best possible ending, when all the Chaos Rings are collected. This fuels speculation that they may have been meant to be in this game.