Boo

The Boo is an item introduced in Super Mario Kart. It makes the user invisible, allowing them to drive off-road. It also steals a random item from another player.

Koopa Kart 64
The Boo makes its Koopa Kart series debut in Koopa Kart 64, where it can be obtained from 4th to 9th place. When used, the Boo will steal the best item in reach and give it to the user while also providing total invisibility and invincibility for a short period of time.

Koopa Kart Advance
The Boo returns in Koopa Kart Advance, serving the same role as in Koopa Kart 64. Like in the previous game, it is obtainable from 4th to 9th place. In addition to stealing items, it will also steal Coins from another racer.

Koopa Kart: Double Trouble!!
In Koopa Kart: Double Trouble!!, the Boo is King Boo and Petey Piranha's Special Item and is obtainable from 5th to 10th place. While it no longer steals Coins, it gives the player a speed and off-road advantage, and it slows down the leading racer.

Koopa Kart DS
The Boo's next Koopa Kart appearance is in Koopa Kart DS. Its overall behavior is much the same as the previous game, though it no longer slows down the leading racer, and it only steals the nearest racer's item. The range for this item ranges from 5th to 10th place.

Koopa Kart Wii
The Boo returns in Koopa Kart Wii, acting the same as it did in Koopa Kart DS. This time, however, it allows the player to drive through obstacles, which provides risk and reward. Due to the addition of 16 player racing per track, it can be obtained from 7th to 13th place.

Koopa Kart Tour
After its absence from Koopa Kart 7 or Koopa Kart 8, the Boo returns in Koopa Kart Tour as King Boo's Special Item, serving the same purpose as in Koopa Kart Wii. As in Koopa Kart: Double Trouble!! and Koopa Kart DS, the item is obtainable from 5th to 10th place.