Exception

Exception (イクセプション) is the true final stage of Sonic Rush. In this stage, Sonic and Blaze use the powers of the Chaos and Sol Emeralds to become Super Sonic and Burning Blaze to fight Doctor Eggman and Eggman Nega, who are controlling a robot known as the Egg Salamander. It is accessible at the character select screen after collecting all of the Chaos Emeralds with Sonic and the Sol Emeralds with Blaze, and completing both their stories. The zone is a multicolored dimensional rift that is the result of Sonic and Blaze's worlds merging together to form one, a place in which both Eggmen hope to build their Eggman Empire in.

Description
The player takes turns in controlling one character a time. First you play as Super Sonic in the top screen who fights Eggman and can only dash with the A and B Buttons. In order to damage Eggman's mecha, Sonic has to deflect the two small satellites that Eggman fires back at his cockpit. After getting hit, Eggman fires some energy beams which can also be deflected back at him. Eggman will occasionally even go into the background and fire rockets which Sonic has to dodge or lose 5-7 rings if hit. He will also attack Sonic using the robot's sword. After three hits, the Eggmen will take to the bottom screen with Eggman Nega now controlling the mecha to fight Blaze.

As Burning Blaze, she can dash like Sonic but only with the B Button, and she can also generate fireballs with the A Button. Nega fires lasers much more quickly than Eggman, and he mainly attacks by using his claws to knock her back. Sometimes, he will hold out a claw and fire it at Blaze. If the player manages to dodge it, it will leave him vulnerable to an attack. If the player fails to attack, Nega will grab Blaze and hit her with the other claw, causing her to lose rings. Other times, he'll go into the background and cause a spatial rift which will not only pull Blaze in, but also any rings nearby. To dodge the rift, the player must dash numerous times until the rift disappears. After getting hit three times, the villains will return to the top screen, and back again. The pattern will continue 5 times.

At the end of the battle, Eggman Nega, still refusing defeat, claims he will succeed, but Eggman starts panicking and tells him to shut up. Then Sonic and Blaze use their combined efforts to destroy the Egg Salamander once and for all. Then Sonic and Blaze say their goodbyes, give each other a handshake, and return to their respective worlds.

As the fight goes on, the background starts to fluctuate changing from yellowish-red to orange to red, and it finally starts fluctuating wildly when near the end. The theme "Wrapped In Black" will go faster.

Trivia

 * This is the only boss stage in the game (aside from the Leaf Storm boss of Sonic's story) where each character fights their own dimensional Eggman, with Sonic battling Eggman, and Blaze battling Eggman Nega.
 * The beginning of the stage is similar to the Doomsday Zone, where Sonic or Blaze must collect rings, avoid asteroids, and dodge Eggman's attacks.
 * The ending theme for this stage is heard in Sonic and Sega All-Stars Racing when completing a race at Final Fortress.
 * This stage could've been an inspiration for the Sonic Generations Time Eater boss, focusing on two people battling in time and space.