Outfit

Outfits, also referred to as Skins and Costumes, are alternative, and often optional clothing that characters can wear, primarily serving as nothing more than aesthetic change.

Sonic Adventure
In Sonic Adventure, upon collecting all 130 emblems, a bonus Metal Sonic skin can be unlocked for Sonic as a reward. The costume, the mostly changing only the appearance of Sonic, will also cause him to hover instead of walk, and it also gets rid of all of his normal voice clips. Item Boxes that contain 1-UPs are also replaced with a Metal Sonic icon.

Sonic Adventure 2
In Sonic Advenutre 2,  several costumes can be downloaded for all 6 main characters; Sonic, Shadow, Tails, Eggman, Knuckles, and Rouge. Each character is given a racing outfit, Halloween outfit, and Christmas outfit. Sonic and Shadow can also wear outfits based on characters from the SEGA franchise, Phantasy Star Online 2. Rouge also has an outfit exclusive to the original dreamcast version that is unavailable in the Gameube port.

These costumes can be unlocked by getting A-ranks on all the missions of each character. However, certain costumes, like the PSO2 costumes, must instead be downloaded.

Sonic Rivals 2
Sonic Rivals 2 provides all 8 of the playable characters with 4 different alternate costumes that can be unlocked by first meeting and completing certain challenges.

Sonic's Outfits

 * Race Suit: Unlocked by running 15,000 M with Sonic
 * Ice Suit: Unlocked by winning the Sonic Cup in single player
 * Black Tie Suit: Unlocked by defeating Shadow 20 times with Sonic
 * Cheetah Suit: Unlocked by winning Sonic Cup in multiplayer

Tails' Outfits

 * Ace Pilot Suit: Unlocked by flying 5 collective minutes with Tails
 * Captain Suit: Unlocked by winning Tails Cup in single player
 * Tiger Suit: Unlocked by defeating Metal Sonic 20 times with Tails
 * Zebra Suit: Unlocked by winning Tails Cup in multiplayer

Knuckles' Outfits

 * Race Suit: Unlocked by attacking any rival 50 times with Knuckles
 * Eggman Suit: Unlocked by winning Knuckles Cup in multiplayer
 * Armor Suit: Unlocked by winning Knuckles Cup in single player
 * Gladiator Suit: Unlocked by beating Rouge in any mode 20 times.

Rouge's Outfits

 * Race Suit: Unlocked by collecting 500 Rings with Rouge.
 * Stealth Suit: Unlocked by winning Rouge Cup in multiplayer
 * Armor Suit: Unlocked by beating Knuckles 20 times with Rouge
 * Raider Suit: Unlocked by winning Rouge Cup in single player

Shadow's Outfits

 * Race Suit: Unlocked by using Shadow's Chaos Control 20 times.
 * Flame Suit: Unlocked by winning Shadow Cup in multiplayer
 * 80's Suit: Unlocked by winning Shadow Cup in single player
 * Mercenary Suit: Unlocked by defeating Sonic in any mode with Shadow.

Metal Sonic's Outfits

 * Mach 3.0 Suit: Unlocked by copying all rivals' signature moves once.
 * Circuits Suit: Unlocked by winning Metal Sonic Cup in single player.
 * Jester Suit: Unlocked by defeating Tails 20 times with Metal Sonic.
 * Mach 2.0 Suit: Unlocked by winning Metal Sonic Cup in multiplayer.

Silver's Outfits

 * Race Suit: Unlocked by using Silver's ESP 20 times on any rival.
 * Lightening Suit: Unlocked by winning Silver Cup in multiplayer
 * Christmas Suit: Unlocked by winning Silver Cup in single player
 * Cyber Suit: Unlocked by beating Espio in any mode 20 times.

Espio's Outfits

 * Race Suit: Unlocked by using Espio's Chroma Camo 20 times.
 * Ninja Suit: Unlocked by winning Espio Cup in single player.
 * Mummy Suit: Unlocked by defeating Silver 20 times with Espio.
 * Knight Suit: Unlocked by winning Espio Cup in multiplayer.

Sonic Lost World
In Sonic Lost World, Sonic can wear an outfit based on Nintendo's Link. However, this costume can only be worn in the Legend of Zelda Zone. The player has no choice in whether they want to traverse said zone with or without the suit, as Sonic will always wear this costume while playing this stage.

Sonic Runners
Several characters wear alternate outfits in Sonic Runners, although they act as separate characters, requiring them to be leveled up on their own alongside their base character. These costumed characters also provide boosts to the base character's bonuses.

All alternate outfits in Sonic Runners, save for Gothic Amy, are exclusive to events, and can't be unlocked otherwise.

Outfits

 * Christmas Sonic: Sonic dressed as Santa Claus. This costume boosts Sonic's normal 50% Distance Bonus to 75%.
 * Christmas Tails: Tails dressed as an Elf worker. This costume boosts Tails' normal 50% Distance Bonus to 75%.
 * Christmas Knuckles: Knuckles dressed as a Reindeer. This Costume boosts Knuckles' normal 50% Distance Bonus to 75%.
 * Halloween Shadow: Shadow dressed as a Vampire. This costume changes his usual 50% score bonus to 75%.
 * Halloween Rouge: Rouge dressed as a Witch. This costume changes her usual 50% score bonus to 75%.
 * Halloween Omega: Omega dressed as a Jack O' Latern, with all the red on his body colored purple. This costume changes his usual 100% enemy bonus into 50%.
 * Gothic Amy: Amy dressed in Gothic cloths. This costume changes her usual 50% animal bonus into 75%.
 * Amitie Amy: Amy dressed as Amitie from the Puyo Puyo series. This costume changes her usual 50% animal bonus into 75%.

Sonic Dash 2: Sonic Boom
In Sonic Dash 2: Sonic Boom, all playable characters excluding Shadow are able to wear christmas-themed costumes