Waluigi

Mario Kart: Double Dash!!
Waluigi makes his first appearance in the Mario Kart series in Mario Kart: Double Dash!! as a playable character. In the game, he is available from the start, and is classified as a middleweight character. The Waluigi Racer is Waluigi's personal kart, and his default partner is Wario. Waluigi and Wario both share a special item, the Bob-omb. He also has his own course, Waluigi Stadium, which is the last course in the Flower Cup.

Mario Kart DS
Waluigi also appears in Mario Kart DS. He is an unlockable playable character. Again, he is a middleweight racer. Waluigi has three karts, which are the Standard WL, the Zipper, and the Gold Mantis. He is unlocked if the player completes the Retro Grand Prix in 100cc. He again has his own course, Waluigi Pinball, which is the third track of the Flower Cup.

Mario Kart Arcade GP 2
Waluigi appears in the arcade game, Mario Kart Arcade GP 2. He is one of the playable all-around racers. Waluigi even has his own cup, the Waluigi Stage. There are only two races, Stadium Arena and Waluigi Stadium.

Mario Kart Wii
In Mario Kart Wii, Waluigi is a starting, playable character. While Waluigi typically is in the middleweight class, he is categorized as a large-sized character in this game, likely due to his tall height. Also, in Mario Kart Wii, Waluigi is given an acceleration bonus that is tied with that of Toad. He also provides a drift bonus and a small off-road bonus. Waluigi Stadium from Mario Kart: Double Dash!! also returns as a retro course in the Banana Cup.

Mario Kart Arcade GP DX
Waluigi later appears in Mario Kart Arcade GP DX, this time as an unlockable character. Unlike the previous games, which have either made him a middleweight or, in the case of Mario Kart Wii, a heavyweight racer, Mario Kart Arcade GP DX places Waluigi as a lightweight character.

Mario Kart 7
Although Waluigi doesn't appear in Mario Kart 7, his course from Mario Kart DS, Waluigi Pinball does.

Mario Kart 8
Waluigi returns in Mario Kart 8 as a playable racer where he is available from the start. While classified as a heavyweight, Waluigi is actually one of the lighter heavyweights, sacrificing some speed and weight to boost acceleration, handling, and grip a little; he shares this trait with Donkey Kong, Rosalina, and Roy Koopa.

Ranking On Character Popularity
With an Γ on his cap, he is considered to be a winner and is the fourth best Mario Kart character of all time, behind Wario, Dry Bowser, and Tanooki Mario.