I've heard of Waliugi and seen him in some clips used in some video game reviews. I'm not sure if he is Wario's brother or just an evil version of Luigi, or both.
Hmmm... one fact is that he appeared the first time in the videogame for N64 "Mario Tennis 64"... and that's all. xD The only thing we can do is to interpret his appearance and his behavior. In the most video games related to Super Mario he is seen with Wario, I think he's the brother of Wario, but that's not confirmed by Nintendo... but I'm not sure. And, the most time, he's evil, but in the videogame "Mario Party 8" he's like a gentleman (maybe Nintendo is trying to make him more sympathetic, because he's not so popular).
And Waluigi doesn't like Luigi. Unfortunately Waluigi hasn't a own videogame yet.
