Omega

E-123 Omega is a character from the  franchise created by Dr. Eggman to contain Shadow the Hedgehog. He first physically appears in the game Sonic Heroes where he, Shadow, and Rouge the Bat team up to form Team Dark. Shadow and Rouge go on to be Omega's closest friends and allies.

His voice is provided by Maddie Blaustein in Mario & Sonic at the Olympic Winter Games and Vic Mignogna in Mario & Sonic at the London 2012 Olympic Games and Mario & Sonic at the Sochi 2014 Olympic Winter Games.

Super Smash Bros. Brawl
In Super Smash Bros. Brawl, E-123 Omega appears as a sticker. It can be applied to any character in The Subspace Emissary to boost their resistance by 17 points.

Super Smash Bros. for Nintendo 3DS
E-123 Omega appears as a trophy in Super Smash Bros. for Nintendo 3DS.

Super Smash Bros. Ultimate
In Super Smash Bros. Ultimate, E-123 Omega appears as a novice spirit.

Mario & Sonic at the Olympic Winter Games
E-123 Omega appears in Mario & Sonic at the Olympic Winter Games as the second rival of the festival mode. He races the player in Speed Skating and has rocket boosters that speed him up drastically. In team festival mode he is not the boss of speed skating and is instead the boss of the Short Track Relay.

During the Adventure Tour in the DS version, Omega appears in Blizland where he challenges Mario and Sonic the Hedgehog to beat him in Intense Short Track. After he is beaten, Omega will reveal to Mario or Sonic that the reason why he came to Blizland was to try to defeat Dr. Eggman, but Dr. Eggman would only accept his challenge if he defeated Mario and Sonic. When he leaves, Toad says he thought Omega would join them.

Mario & Sonic at the London 2012 Olympic Games
In the Wii version of Mario & Sonic at the London 2012 Olympic Games, Omega appears as one of the rivals in London Party Mode. When the player first encounters him, he challenges them to the 100m, and rematches them in the 4x100m Relay, which he runs by himself rather than with a team. A Mii outfit based on Omega can also be unlocked.

In the Nintendo 3DS version, Omega appears in the story mode, where he challenges Donkey Kong in Wrestling - Freestyle while on a rampage. During the match, Donkey Kong manages to knock a control chip out of Omega that was installed by Dr. Eggman, causing Omega to apologise for his behaviour but revealing that his memory has been wiped due to it. After Tails and Espio explain about Bowser and Dr. Eggman's plan with the Phantasmal Fog, Donkey Kong suggests that Omega should go with Tails and Espio to help stop Dr. Eggman, and Omega agrees, following them to the Main Stadium and explaining what happened. When the fog returns, Omega suggests that they investigate Stonehenge after recovering some of his memory, and while at Stonehenge Omega remembers Magikoopa giving him something, so the group ask Magikoopa about it. When Magikoopa loses a challenge to Sonic, he uses magic to fire Omega away, causing him to remember details about the Fog urn, find the urn's lid and reveal Bowser and Dr. Eggman's location. The group then head to Big Ben, but Omega and Toad return to the Main Stadium as they are struggling to continue with the thick fog. Omega later calls Mario, Luigi, Sonic and Tails from the Main Stadium to support them when they challenge Bowser and Dr. Eggman, and later appears at the opening ceremony. A badge of Omega can also be obtained from the badge machine.

Mario & Sonic at the Sochi 2014 Olympic Winter Games
E-123 Omega appears in Mario & Sonic at the Sochi 2014 Olympic Winter Games as one of the rivals in the Legends Showdown mode. He is found in Area 5, and is raced against in Roller Coaster Bobsleigh.

Mario & Sonic at the Rio 2016 Olympic Games
Omega returns in the Nintendo 3DS version of Mario & Sonic at the Rio 2016 Olympic Games, this time as a playable character (although, like Dry Bowser, he is only playable in the Javelin Throw and Javelin Throw Plus events). This marks his first playable appearance in the series.

Trivia

 * Omega is the only rival in Mario & Sonic at the Olympic Winter Games to appear in two different locations. In Festival Single mode, he appears at the Olympic Oval, and in Festival Team mode, he appears in Pacific Coliseum.
 * Omega is the only new playable character in Mario & Sonic at the Rio 2016 Olympic Games to appear in story mode and not be competed against.