SOS Missions are a gameplay feature that appears in Sonic Forces. They are additional, optional objectives that the player can choose to complete. Completing SOS Missions will allow the player to unlock Avatar items as a part of their Challenge Mission rewards.
SOS Missions are optional tasks that the player-controlled characters in Sonic Forces can complete in so-called "SOS Stages". SOS Stages are regular stages in the game that have been chosen to be the sites of these Missions. In the context of the game's storyline, SOS Missions represent SOS signals from members of the Resistance that are in need of help. SOS Missions are only available if the player has an online account to PlayStation Network, Xbox Live, Nintendo Online, or Steam to get access to renting Avatars, checking their online ranking, and receiving SOS Missions.
SOS Missions come in three kinds, each one represented by one of the following colors:
Red: In these Missions, the player must clear a SOS Stage using a brand new Avatar different from the player's own (the player's own Avatar will not be available), presumably one of the Rental Avatars available at the time. The new Avatar will be the one that sent the SOS signal. Along with the new Avatar, the player is also given a different Wispon for the duration of the Mission.
Green: In these Missions, the player must clear a SOS Stage while using a Rental Avatar (an Avatar with their own independent Wispon that the player can swap out with their own during gameplay). The Rental Avatar will be the one that sent the SOS signal.
Blue: In these Missions, the player must use either Modern Sonic, Classic Sonic, Shadow or their Avatar to search the SOS Stage for a Capsule containing the Avatar that sent the SOS signal. Once the Capsule is found, free the trapped Avatar and clear the SOS Stage in order to complete the Mission. In addition, the Capsules vary in locations, meaning the player will not normally find it in the same place twice in a stage.
SOS Missions will start appearing on the World Map screen (also known as the stage select screen) after clearing Green Hill. A SOS Mission becomes available at random after completing a stage or exiting a menu. The color of the SOS icon next to the Stage Target for the SOS Stage indicate the Mission's type.
If the player loses a life, quits the game or clears the SOS Stage without rescuing the Avatar in the case of the blue SOS Missions, the player will fail the Mission without the option to retry. Exiting to the Main Menu will also remove all SOS Missions on the World Map.
While playing an SOS Mission, the player can still collect Red Star Rings, Number Rings and Silver Moon Rings that have not already being collected and should the player complete the SOS Mission, all collectible items are saved but if the player fails the Mission in the aforementioned methods, those collectibles will be lost.