Knuckles' Chaotix, known as Chaotix (カオティクス Kaotikusu) in Japan, is a platform game developed by Sonic Team and published by Sega for the Sega 32X in 1995. It is a spin-off to the Sonic the Hedgehog series, and the only one to be released for the system. It is also one of a few that does not feature Sonic himself. Instead, the game centers around Knuckles the Echidna, and the Chaotix team of characters as they try to stop Dr. Robotnik and Metal Sonic from their evil plans. Gameplay is similar to earlier Sonic titles, however, the game introduces a partner system in which the player's character is connected to another via a ring force bond with "rubber band" physics. Most of the gameplay is based on using this mechanic to maneuver the characters through the stages.
Upon release, Knuckles' Chaotix received mixed reception, with most of the criticism directed towards the level design and partner system. However, the game remains one of the most popular titles in the small 32X library. Contrary to most other classic Sonic titles being re-released in modern video game compilations, Knuckles' Chaotix was only re-released through GameTap's PC service for a brief period in 2007.
The primary objective of the game remains unchanged from previous Sonic titles. The player must finish each level in under ten minutes and defeat Dr. Robotnik's badniks along the way. Rings still constitute the player's life energy and can be collected to enter special stages. If the character has no rings, getting hit will temporarily cause the player to lose his partner, who will return eventually, effectively making the partner an extra hit point. If the player is damaged when he has no rings and his partner is absent, he will automatically be taken out of the level, requiring the player to restart their progress with the level. Unlike previous games in the series, there are no "lives". The game cartridge features battery-backup saving, which allows the player to save their progress either manually (by passing the Exit sign) or automatically (after clearing an Act or Special Stage).
The game comprises 5 worlds (called Attractions), each with 5 levels. Levels are set at different times of day (morning, day, evening and night), which are determined by the time spent in the previous level and affect enemy placement and boss difficulty. At the end of Level 5, the player confronts Dr. Robotnik in one of his contraptions.
The most fundamental change in Knuckles' Chaotix how multiple characters interact, which involves two characters being connected with an elastic bond. Both players are connected on one single screen while neither player acts as the dominant force to move the game forward. In addition to character's individual abilities, other tricks can be executed with the elastic force of the ring bond. For example, player 1 can hold his position while player 2 runs forward and stretches the bond to gain maximum speed, creating a sling shot effect. In mid-air the bond can be used to generate upward momentum. Additionally, players can toss each other toward platforms or use the call-button to reunite (at a cost of ten rings).
The bonus stage can be accessed by collecting 20 or more rings and jumping through one of the large rings found hidden throughout a level. In the stage, the character free-falls down a long spiral of rings, power-ups, blocks and exits while the player's rings gradually count down to 0. The stage ends when the ring count reaches 0 or when the character hits an exit. Possible bonuses include a slow-down at the attraction roulette screen or a free pick from the Combi Catcher.
In the special stages, the player moves his character through a hexagonal, fully rendered 3D course to collect a specified set of blue spheres. Rings are collected as seconds and when the count reaches zero or the player falls from the course, the stage ends. When successfully completed, the player is awarded one of six Chaos Rings. Collecting all the Chaos Rings awards the player with the best ending. Special stages can only be accessed through a single large ring at the ending of each level, but the player must have collected at least 50 rings for it to appear. The starting ring count that is used as time in the special stage is based on the amount of rings collected in the previous stage (if a player collects 180 rings, then the player will have 180 rings/seconds in the special stage; however, if a player has more than 200 rings at the end of the stage, then the player will start the special stage with 200 rings/seconds). After a player wins all six Chaos Rings, the special stages start over in a wireframe mode.
The story varies between the Japanese and English releases of the game. In the Japanese manual, a mysterious island rose from the sea shortly after the events of Sonic & Knuckles. Dr. Eggman discovered the island, and found a mysterious ring inscribed with descriptions of the "Chaos Rings", ancient Rings infused with Chaos Emerald energy. Robotnik builds his base on the island in hopes of harnessing their power, alongside hopefully getting closer to the all-powerful Master Emerald. He, with the help of Metal Sonic, captures new characters Mighty the Armadillo, Espio the Chameleon, Vector the Crocodile, and Charmy Bee upon their arrival at the island as well. Knuckles, curious about the strange island, goes there as well, and manages to rescue Espio. The two then go on to save the other characters and stop Eggman from getting the Chaos Rings.
In the English manual, Knuckles guards Carnival Island, a large high-tech amusement park. Dr. Robotnik goes there to find the Power Emerald that supplies electricity to the whole island so he can use it to fuel his evil devices. Dr. Robotnik traps Vector, Charmy, and Mighty, who were visiting the island, in his Combi Confiner that freezes them in time and is about to do the same to Espio the Chameleon until Knuckles chases him away. Knuckles then discovers that he can rescue one friend at a time using Ring Power, which holds the two partners together like a rubber band. All the characters then work together to save Carnival Island from Robotnik before tomorrow's grand opening.
The group travel through the island's "attractions", fighting Robotnik and his machines along the way. After finishing all levels, the Chaotix arrive back at the game's main hub, only to discover that it has been hijacked by Metal Sonic.
The Chaotix fight and defeat him, destroying the world entrance in the process. Metal Sonic is severely damaged, so Robotnik transfers his CPU to a larger, tougher body using the seventh Chaos Ring, trapping the Chaotix in a small room with the enhanced Metal Sonic. After another fight, the team manages to defeat him again. The ending depends on whether or not the player collected all of the Chaos Rings. If they are not collected, Metal Sonic is seen burning an entire city. If they are, however, Robotnik and Metal Sonic are repelled, and the Chaotix are seen standing in front of the peaceful city with Sonic and Tails.