Secret stage

Secret stages are six extra, optional stages in Sonic Forces. Unlike regular stages, secret stages first become available after the player reclaims a territory on the World Map. Finishing a secret stage will reward the player with extra Costume Parts and bonus experience for the Avatar.

Overview
Secret stages have the same gameplay mechanics as regular stages in Sonic Forces and have the same objectives (reaching the goal within a time limit). Secret stages however, are much shorter than regular stages. They are also always played from a 2.5D perspective and their gameplays put emphasis on a particular gimmick or obstacles, such as flamethrowers or bomb-based blocks. The routes the player travels along in a secret stage are likewise different from those in regular stages, having been construction from the ground up with additional plaforms and basic building blocks, like unbreakable Containers.

Secret stages are unlocked after the player reclaims an area from the Eggman Empire. This occurs after the player completes a specific stage during the main playthrough. It is also worth noting that only Sonic the Hedgehog and the Avatar are playable in the secret stages. Shadow the Hedgehog also becomes playable in them if the player has downloaded Episode Shadow.

On the World Map (the stage select screen), the Stage Targets (the markers that indicate a stage's position on the World Map, along with the available character for the stage and the player's current ranking for it) for secret stages look like round padlocks.