From the Super Mario Wiki
Big the Cat is a character in the Sonic the Hedgehog series, as well as a referee in Mario & Sonic at the Olympic Games. Appearing in very few events, Big the Cat watches over the game matches held. He mainly appears in the Athletics and Rowing events, but is rarely seen anywhere else. Additionally, in the awards ceremonies of the Athletics events, Big the Cat can be seen in the background. Big the Cat is accompanied by Cream, Espio, and Charmy Bee as Sonic series referees.
Although he never made a physical appearance in Super Smash Bros. Brawl, Big showed up in a Sticker.
He also appears in Mario & Sonic at the Olympic Winter Games as a cameo VIP character in the Wii version. However, he plays a more important role in the DS version's Story Mode. He is found in Polastraits, wondering what is the "sign" near him. Amy Rose tries to explain that each mission's details is written there. However, Big still doesn't understand and Amy had to try out the mission and complete it to make him understand. When she does, he rewards the player with a Spark Luge. The mission Amy has to take is Alpine Skiing GS.
Super Smash Bros. Brawl Sticker
|| Sonic Adventure Director's Cut
|| Battering Resistance +14
Super Smash Bros. for Nintendo 3DS Trophy
|Big the Cat
||Big the Cat spends most of his days in peace with his best friend, Froggy. But he's no ordinary cat! He enjoys napping, eating, more napping...um... He also likes fishing, which tests his strength. And if Froggy is ever in danger, Big won't even think twice before helping!