Mini Mushroom

The Mini Mushroom is a variety of Mushrooms found in the Mushroom Kingdom. Whoever uses it will shrink greatly in size, becoming as tiny as a mouse and sneak into smaller areas.

Mario Party 4
The Mini Mushroom debuted in Mario Party 4 as a pink capped mushroom with what appears to be a pacifier that reduced the Dice Block from 1-10 to 1-5 and allowed a person under its effects to enter Gates and play Mini Mini-games. Additionally, it had an alternate form called Super Mini Mushroom, colored entirely translucent pink, that did the same, but with two Dice Blocks.

Mario Pinball Land
They got a short reappearance in Mario Pinball Land, where they could let Mario go into small places and get extra Power Stars. They usually cost ten coins and took their Mario Party 4 look.

New Super Mario Bros.
They reappeared in New Super Mario Bros., where they were a shade of blue, and they shrunk Mario's and Luigi's size greatly and yet again gave them the ability to enter tiny Warp Pipes. They also gained the abilities to perform Floaty Jumps and run across water, thanks to their very light weight. Unfortunately, one hit will cause a Mario brother to lose a life. If Mario or Luigi (in Mini form) is able to defeat the Mummipokey, then he will gain access to World 4. If he beats Petey Piranha in Mini form, he can go to World 7.

New Super Mario Bros. Wii
They appear again in New Super Mario Bros. Wii. They are just like the mini mushrooms from the original New Super Mario Bros. However, they are not used as often and are in fact rarely seen in levels, but they can be found in Mushroom Houses.

Trivia

 * A different kind of mushroom, called a Poison Mushroom, works similar to the mini-mushroom. However, in some games, it will take out the player if he/she is small.