Sega has accidentally leaked the changes included in Sonic Mania Plus via an update to the original game on PlayStation 4.
Sonic Mania Plus is an upcoming physical release of the excellent 2017 reboot/compilation on Switch, PS4, Xbox One and PC. The updated release plans to include two new characters in the form of Mighty the Armadillo and Ray the Flying Squirrel.. A new Encore mode will also be included alongside a range of updates to the core game. These changes have apparently been leaked as a patch for the original game arrived unintentionally on PS4. Fortunately, Twitter users were able to capture images of the update game including secret options and a DLC tab on the main menu (indicating the Encore mode will be paid DLC for owners of the base game).
Streamer Raikou also recorded footage from the updated game, showing off new transitions added to the stages that were missing them and a new Robot Sonic bossfight phase. Other changes includes the ability to disable the time limit for stages and use unlockable abilities on Save Game files.
Sonic Mania Plus is currently planned for a Summer 2018 release, with the physical release including a 32-page art book