Boost Mode

Boost Mode (ブースト Boost) is a special mode engaged in the Sonic series. Sonic, Miles Prower, Knuckles, Amy Rose, Cream, Cheese, Blaze, and Super Sonic have been seen entering it. Also, although Shadow has never been seen using it, considering he can run as fast as Sonic with his jet shoes, he may possess the ability as well.

Purpose
If a character can use the ability, then he/she is able to run at extremely fast speeds, usually leaving afterimages of the character. That's basically what it does, but it may have different effects based on the game it appears in.

Sonic Advance 2
In this game, the character is simply able to run fast. The more rings the player has obtained, the faster the character can enter the mode. If the character slows down or is hit by an enemy, then the boost is automatically ended. Sonic can also engage this manually if he performs a failed Homing Attack and hits the ground running. For the entire duration of the move, the character can perform a Boost Attack which varies depending on the character.

Sonic Advance 3
This is basically the same as in Sonic Advance 2, but without the Boost Attacks. However, only speed-based teams are able to use it. If Sonic is the character's partner, he/she can manually engage it via Tag Action. However, if the character is partnered with Cream (except for Amy) and performs a failed Homing Attack and hits the ground running, then he will automatically enter Boost Mode.

Sonic Rush and Sonic Rush Adventure
Sonic and Blaze not only can enter this mode by running fast, but also can manually engage it. If they manually engage it, then they are able to run even faster than the original boost mode. This form of boosting is known as the "Super Boost". In order to engage the Super Boost, however Sonic/Blaze must fill a gauge known as the "Tension Gauge" to do it. It can be filled by collecting rings, performing tricks, and defeating enemies. Then, when the gauge has energy in it, by pressing the X button, Sonic/Blaze will go forward at high speeds, blasting through enemies in their path. This may have been a replacement for the classic Spin Attack, which would also send the player to their top speed (though the Spin Attack is still in the game).