Use your collected items to customize your Avatars! Never underestimate the importance of personal appearance! — Amy Rose, Sonic Forces instruction manual
Costumes, also referred to as Parts, are objects that appear in Sonic Forces. They are outfits and accessories for the Avatar that the player can use to customize their Avatar's outward appearance.
Costumes are basically different pieces of clothing and accessories for the Avatar to wear. They come in hundreds of different colors, shapes, and types. However, there are typically three copies of each distinct Costume piece, each one with a different color scheme.
In Sonic Forces, the Costumes are used in gameplay to customize the Avatar's appearance in stages and cutscenes. Like the typical Outfits, the Costumes have no impact on the gameplay in the various stages. Each Costume piece falls into one of the categories below, which may include the following:
The game features over 700 different Costume parts for the Avatar. Costumes can be added, swapped and removed at the player's leasure and can be combined with any other Costume available to the Avatar. Costumes are not limited by gender either, as a male Avatar can wear Costumes designed for females and vice versa. However, the Avatar can only wear one Costume part from one Costume category at any given time. At the beginning of the game, only a few Costumes will be avilable to the player. By completing Challenge Missions however, the player can unlock more Costumes. When earning them from completing Challenge Missions, the Costumes will temporarily pop up on the Result screen that appears after the player completes a stage. Some Costumes are also available through DLCs.
Between stages, the player can customize the Avatar with the Costume parts in the Fitting Room on the Avatar screen. When a new Costume is added to the Avatar screen, it will be marked with a red "!" symbol until it has been looked up. The player is also able to save their outfit combinations in the Closet on the Avatar screen, which can hold up to fifteen outfit combinations.
Unlike male Avatars, a customizable bodysuit was made mandatory for female Avatars to make the game suitable for younger ages. Despite this, the bodysuits that change the Avatars fur color will show them without it.