Thunderbolt
In Mario Kart
In the Mario Kart series, Thunderbolts are extremely powerful items that racers usually receive when they are in (or near) last position in a race. When used, a Thunderbolt will temporarily shrink all the other racers, making them slower, lighter, and chipmunk-voiced.
In Mario Kart 64 if the player runs over a player who is small while he or she is big, they will be squished for a while. If two small people run into another they both will be squished. If they hit an obstacle such as a Thwomp they will be pushed back and be squished.
In Mario Kart: Double Dash!! it will not affect the player if he or she is currently indisposed (such as having just been hit by another item or fallen off a cliff).
In Mario Kart DS and Mario Kart Wii, the effect of being hit by a Thunderbolt wears off quicker the lower in the rank you are. For example, someone hit by one while in 7th/11th place will return to normal almost immediately, while those in 1st or 2nd place will remain shrunk for much longer. Also, the background music of the track will be sped up and raised in pitch. In Mario Kart Wii, a racer who was super-sized from using a Mega Mushroom would be returned to normal size when struck by the Thunderbolt instead of shrunken completely.
In other games
The Thunderbolt was an item featured in Super Smash Bros. Brawl. If a fighter touched it, either they would shrink, their opponents would shrink, or their opponents would grow.