Sonic Mania/Unlockables

Super Peel-Out and Insta-Shield
The Drop Dash is a feature meant to give classic Sonic fans a fresh experience, but if classic Sonic fans prefer a more authentic old school experience, then two special abilities from fan favorite Sonic games have made a return in the form of unlockables. The Super Peel-Out from Sonic CD is similar to the Spin Dash in that once charged, it launches Sonic forward at high speed, indicated by the infinity shape that his feet form. However, unlike a Spin Dash, the Super Peel-Out leaves him vulnerable to enemy collisions. It can be performed by holding.
 * How to unlock: 1 Medallion for Super Peel-Out, 6 Medallions for Insta-Shield

While the Super Peel-Out offers flashy speed, the Insta-Shield from Sonic 3 offers safety in the form of a temporary shield that forms around Sonic in mid-air. Performing a double jump will cause a shield to flash around Sonic, giving him temporary invincibility against enemies that ordinarily would not be affected by a Spin Jump. This can come in handy particularly for bosses. To activate either ability after having unlocked it, enter the options menu via file select in Mania Mode.

& Knuckles Mode
You can now have Knuckles follow you around, even when playing as Knuckles. This can be activated in the options menu via file select in Mania Mode after it's been unlocked. Surprisingly enough, if you have this activated while playing Knuckles and have collected all seven Chaos Emeralds, Egg Reverie can be accessed as Knuckles. Clear the zone for a secret alternate ending.
 * How to unlock: 11 Medallions

Debug Mode
This wouldn't be a classic Sonic game without its very own Debug Mode. Debug Mode allows you to essentially break the game, placing helpful items wherever you please. To enter item placement mode during gameplay, press ;  allows you to cycle through items and if the chosen item is an Item Box,  allows you to decide what type of Item Box. Finally, press to place the item. Like Sonic's alternate abilities and & Knuckles Mode, Debug Mode can be activated by entering the options menu via file select in Mania Mode.
 * How to unlock: 16 Medallions

Mean Bean and Blue Spheres
These mini-games become playable at any time once unlocked in the Extras menu. For Mean Bean, you have the option of playing against the computer or another player. For Blue Spheres, you have the option of playing through the game's original stages (which you'd have to clear to unlock this) or trying out the new Mania stages. The Mania stages add some tricky new obstacles to these stages, such as spheres that must be stepped over twice or spheres that teleport you to different locations. If you happen to be looking for more of a challenge after having cleared the game's original Bonus Stages, this should be worth a try.
 * How to unlock: 21 Medallions for Mean Bean, 32 Medallions for Blue Spheres

Sound Test
The game's Sound Test is unlocked under the name "D.A. Garden" and can be found, like Mean Bean and Blue Spheres, in the Extras menu. This allows you to view the name of and listen to every track in the game while accompanied by a little animation.
 * How to unlock: 26 Medallions

Level Select
While clearing the game will allow you to replay any level on that file (by scrolling through the zones on the file select screen), there's a way to access a classic version of this old school Sonic tradition. While on the file select screen in Mania Mode, enter the game options menu and activate Debug Mode. Then, exit the options menu and press an extra button while starting a No Save game. This will take you to a screen where you can select any act of any zone to play, and even offers a sound test (though the tracks aren't named here). Use to select a character,  to have Tails follow along when playing Sonic, and  to play the selected level.