The Waluigi wah comes from Waluigi, Nintendo's lanky purple rival character who appears mainly in Mario spin-off games. His exaggerated voice clips became a meme online because the delivery is weird, punchy and easy to recognize instantly. Over time, fans clipped the sound into short reaction edits, gaming videos and absurd comedy posts, where it fills a similar role to goofy ahh sounds. It still gets used because the joke lands fast and even non-gamers often recognize the character's vibe.