(there's mods for Project M that add him and the actually pretty good Super Smash Flash 2 fan game has him as a fighter though, his moveset is very fun imo, that fan game has some really well done new characters imo, and are all really fun, so is Chibi-Robo, Ichigo from Bleach, Naruto and Krystal from Starfox are all really fun, I used to play that a lot)
Is Waluigi in the Warioware games? I never actually played those
Strangely, no. He's only in sports and party games so far.
And as an assist trophy in Smash...
(there's mods for Project M that add him and the actually pretty good Super Smash Flash 2 fan game has him as a fighter though, his moveset is very fun imo, that fan game has some really well done new characters imo,
and 
are all really fun, so is Chibi-Robo, Ichigo from Bleach, Naruto and Krystal from Starfox are all really fun, I used to play that a lot)