From Sonic Retro
By pressing and holding any jump button in midair after jumping, Sonic will charge up the move, and will instantly dash off in a short burst upon landing. However, the move cannot be performed if Sonic takes damage before landing, or if an elemental Shield is active. If the move is executed by Super Sonic, a mini-earthquake is set off and the boost will be greater.
After collecting enough medallions in Sonic Mania's Bonus Stage, this move can be replaced with the Super Peel-Out or the Insta-Shield by selecting the appropriate option from the Secrets menu. These options were originally only available on a "No Save" playthrough; however, as of v1.04 they are also available for use on saved files. The player can also use all three moves at once by inputting a cheat code on the secret level select screen.