Thunder Cloud

The Thunder Cloud, also known as the Lightning Cloud in Europe and Australia, is an item introduced in Mario Kart Wii. In the arcade games, it can be thrown to strike another player with Lightning. In Mario Kart Wii, it acts similar to the Time Bomb, but it shrinks the one who has it instead of blowing them up. The item has recently returned in HammerBro101's fan-made installments of Mario Kart.

Mario Kart Wii (2008)
The Thunder Cloud is first seen in Mario Kart Wii. It is the only item in the game that activates itself once obtained from an Item Box and makes a buzzer sound. The item can be obtained anywhere from 3rd to 7th place, with it also being possible to obtain it in 8th place in VS Races.

Koopa Kart Wii (2010)
The Thunder Cloud (called the Lightning Cloud in this game) is a new item to the Koopa Kart series in Koopa Kart Wii, where it can be obtained from 4th to 9th place. As in Mario Kart Wii, the Thunder Cloud will activate automatically upon being obtained. The item will give the player a speed boost and an off-road advantage, but it will shrink the player after having it for exactly ten seconds, affecting the player in the same way as Lightning. The cloud, however, can be passed to another racer by bumping into them. It can also be destroyed if the player gets shot out of a cannon or uses an invincibility item (a Star, Mega Mushroom, or Bullet Bill).

Koopa Kart Tour (2020)
After skipping out on Koopa Kart 7 and Koopa Kart 8, the Lightning Cloud returns in Koopa Kart Tour with its original function, though it can be activated manually and lasts for twenty seconds as opposed to ten. It can be obtained from 3rd to 7th place.

Trivia

 * Like the Mega Mushroom and POW Block, the Thunder Cloud has been absent from two Mario Kart games, spanning an 11 year absence from Mario Kart Wii (2008) to Mario Kart Insanity (2019).