From the Super Mario Wiki
E-123 Omega (Ω) is a character from the Sonic the Hedgehog series created by Dr. Eggman to contain Shadow the Hedgehog. He appears in Sonic Heroes where he, Shadow, and Rouge the Bat team up to form Team Dark.
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 one of the Stickers that gives the player +17 resistance.
Mario & Sonic series
Mario & Sonic at the Olympic Winter Games
E-123 Omega in 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
Omega appears as one of the rivals in London Party Mode in the Wii version of Mario & Sonic at the London 2012 Olympic Games. When the player encounters him, he challenges them to the 100m Sprint so as to prove his speed. If encountered again after being beaten, he challenges the player to a rematch, this time in the 4x100m Relay. In the latter event, Omega runs the entire event on his own, instead of with a team like the player.
Omega appears in the 3DS version as a rival in the Wrestling-Freestyle event.
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.
Super Smash Bros. Brawl Sticker information
||[Flame] - Resistance + 17
Super Smash Bros. for Nintendo 3DS Trophy
||E-123 Omega is, as his name implies, the 23rd robot in Dr. Eggman's E-100 series. Designed to be Eggman's secret weapon and contain Shadow the Hedgehog, Omega instead turns rebel and teams up with Shadow to undermine the villain and create chaos.
- 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.
E-123 Omega at the Sonic News Network
E-123 Omega on Sonic Retro