Thunder Cloud

The Thunder Cloud (also called Lightning Cloud) is an item from the Mario Kart series, appearing in Mario Kart Arcade GP, Mario Kart Arcade GP 2, and Mario Kart Wii. Unlike other items, it activates itself automatically when obtained from an Item Box.

When obtained, the player automatically receives a constant boost of speed. Also, drivers with a thunder cloud won't slow down when they go offroad. However, the Thunder Cloud eventually strikes and shrinks the player. The Cloud, however, can be passed on to another kart by bumping into any other racer before the lightning strikes. To use the item efficiently, racers have to bump another player and let her or him be shrunk instead. It can be destroyed when the character holding it drives into a cannon, uses a Star or a Mega Mushroom.

Trivia

 * This item works similarly as the Time Bomb from Mario Kart Arcade GP and its sequel. However, it shrinks opponents to a small size rather than explode.
 * It is possible that the cloud Lakithunder rides on is a Thunder Cloud, as they both shoot thunder.