Ok, I will be the good guy now...
I remember in Mario Party 3 that Waluigi used Piranha Plant as his partner in Duel mode. Also, he wants to be the owner of the Mischief Star Stamp (he evens defeats Bowser to own it). His favorite item was the Poison Mushroom. He have his own stage called Walugi's Island.
The Waluigi's Island features lots of Piranha Plants, so I do'nt even know what to say about Waluigi using Piranha Plants to his side by now... There was a big bomb in the center of the stage. Here is a image of the board:
In Mario Party 7, his special orb was the Vacuum Orb, used to steal the coins of other opponents.
Also, I can't remember, but after some point in the Mario Party series, Waluigi starts to hold Roses with thorns for his poses.
The special ball of Waluigi in Mario Superstar Baseball is the Liar Ball, but I don't know all the details... I never played Mario baseball games...also, he have the Laser Beam and Super Jump abilities in field. And he is high related with eggplants (wtf) in this game.
In the sequel (Mario Super Sluggers), he can use the Liar Swing. The only thing I know is this is a high risky-high reward move.
In Super Mario Strikers, his legend says: "Waluigi's ego tends to be his biggest enemy", pretty interesting. He is the offensive type captain.
His superstrike is the Drop Rocket, he makes a karate pose and kicks the ball with both foots, and the balls leaves a trail of a purple nebulous cloud.
In the Mario Strikers Charged sequel, he changes to be a defensive type captain. In his mega strike he uses a purple thorn whip. And on his special move called WALL-Luigi he leaves a trail of thorn purple vines.
In Mario & Sonic series, he is a skill type character in all installments
In Mario Sports Mix, he is Technical character type (note that Tricky character category exists , but he is in the Technical one...). His special ability involves a mechanical 4 arms thing that have electric powers.
Also, mentioning Mario Kart 7, he is not a playable character, but a returning stage from the Mario Kart DS returns and is the Waluigi Pinball stage.
I will make another post with more information later... I'm too lazy...