That's how you introduce a character, even if it's not official. Waluigi might only join the battle in Super Smash Bros. Wii U as an assist trophy, but to ease the pain, modder Apoc Hedgie made his own version of Luigi's skinny rival.
He's called Walurambo, and he's the perfect combination of Rambo and Waluigi (and a little bit of Captain Falcon). The Wii Fit trainer would be proud! Here's an intense clip showcasing the character:
Brawl Character Showcase - Walurambo [Apoc Hedgie, YouTube]