Silver

Silver the Hedgehog is a hedgehog from the future who has the ability to use psychic powers.

Super Smash Bros. Brawl
Silver the Hedgehog made a cameo on the Green Hill Zone stage along with Tails and Knuckles. He also appears as a trophy and a sticker in the game.

Mario & Sonic at the Olympic Games
He was originally supposed to appear in the original but was scrapped later on. A beta file of Silver was found on the European version.

Mario & Sonic at the Olympic Winter Games
Silver appears in Mario & Sonic at the Olympic Winter Games as a skill playable character. He was confirmed to appear on the GamesCon 2009 trailer.