The Thunder Cloud is an item in Mario Kart Wii. It has both a positive and negative side. Once you've gotten it, it will appear above you. Although you may drive faster and have the ability to drive off road, you will soon be zapped with lighting. Once this happens you are a shrunk car the size of an ant. Thunder Clouds are always gray and the lightning will flash. It will flash faster and more times as well telling you, that it must be remover. To get it off simply bump into someone.It will go to that character. You can then watch and laugh as that opponent is small. If you're leading the line, then you might have to let the opponent in 2nd place pass you and bump into them. The game warns you when someone with a Thunder Cloud is coming.