Sonic's size in comparison to a Star Post when using Scale
Shrinks Sonic's size and allows infinite jumps
Scale is a move used by Sonic the Hedgehog, which has only appeared in Sonic the Hedgehog (2006) as one of his custom moves. This move shrinks Sonic's size and allows him to perform jumps without limit. This move can only be used when Sonic possesses the Purple Gem.
To use Scale, it is required that Sonic is in the possession of the Purple Gem upgrade. To allow use of Scale the player then has to select the Purple Gem with the directional pad, and to execute it, the player has to press Right Trigger/R1 button.
When using Scale, Sonic shrinks down to a fraction of his size and remains in size for as long as the activation button is hold down. In this state, Sonic runs automatically, similar to Auto Running, but his speed and jumps are increased proportionally to his size, allowing him to cross the same distances in the same time and reach the same heights when jumping as he could in his regular size. If the player wants to stop Sonic from running, they have to briefly push the control stick in the opposite direction.
The main gimmick of Scale however, is that it allows Sonic to perform jumps in midair and without any limit to his jumps. Once Sonic jumps into the air, he can jump again (by pressing the jump button while in the jump) and again, allowing him to make an infinite chain of jumps, for as long as desired and control his direction. For each well-timed jump it will cause Sonic to go higher and higher into the air.
While this move is great for exploring the stages in the game, it is also one of the game's most "broken" features, as it allows the player to easily leave and break the game's limits and set boundaries, such as leaving the stage's field and prevent shifts with other characters during gameplay.