The clip comes from Toad, the cheerful mushroom-headed racer from Nintendo's Mario series, as heard in Mario Kart Wii. Toad's high, squeaky voice has been a trademark of the character for years, and short voice lines like this one are easy to lift, share and reuse. Once uploaded to soundboards, the 'oh yeah' became a handy reaction for gaming clips, streams and memes, especially among Mario Kart fans. It endures because it is instantly recognisable, very short and unmistakably celebratory, making it a quick way to signal a win without explaining the joke.