Super Mushroom

A Super Mushroom is a red Mushroom that serves a particular function depending on the game in which it is found.

Super Mario Bros. series
In Super Mario Bros., Super Mario Bros.: The Lost Levels, Super Mario Bros. 3 and New Super Mario Bros., the Super Mushroom confers the Super status on Mario or Luigi.

In the first game it appears in, Super Mario Bros., the mushroom appears differently, having no eyes and a yellow/red color scheme as well as being shaped more like an actual mushroom.

The next game they appear in is Super Mario Bros. 2. They only appear behind doors or in vases. The still have the exact same effect, only this time they also add to your heart meter.

Donkey Kong
Super Mushrooms also made an appearance in Donkey Kong '94 for the Game Boy. They were used by Donkey Kong during the final battle. He ended up using several of them to transform himself into a giant. A Super Mushroom was also briefly seen in the ending when Pauline gave one to Mario, so that he could change his size and catch Donkey Kong when he was falling.

Hotel Mario
The Super Mushroom appears in Hotel Mario. It doesn't make Mario big or small, but gives him the chance to take one hit and not lose a life. The only difference between the normal Mario and the one that ate the Super Mushroom is the color of his overalls.

Mario Kart Super Circuit
In relation to Mario Kart, a Super Mushroom is an item that gives the kart continuous bursts of speed over a time period of around eight seconds. A particular Super Mushroom is known as the Golden Mushroom can be used over and over. In some games and tracks, it is necessary to clear some (optional) jumps. Hitting another player during the boost allows players to steal any items in some games, or a balloon in Battle Mode's Balloon Battle the other kart may be carrying (in Mario Kart Double Dash!!, if both characters have something, then the player will steal the back player's item and have the front one drop their item).

Mario & Luigi series
In Mario & Luigi: Superstar Saga, Super Mushrooms restore fifty HP to whoever eats one. However, in the game's sequel Mario & Luigi: Partners in Time, a Super Mushroom only recovers fourty HP.

Super Mario 64 DS
In Super Mario 64 DS, the Super Mushroom worked differently, similar to the effect of the Mega Mushroom. The player went to a large size and could destroy most things in their path. If any enemies were defeated after the first seven, then they would get 1-Ups.

Super Smash Bros. series
In Super Smash Bros. Melee, the Super Mushroom allows the player to grow to an incredible size, thus making him/her heavier and harder to knock off. Experiment with them in Huge Melee mode. Use one while playing as Mario, then do his stance. This will make him taller than almost all the levels in the game.

In Super Smash Bros. Brawl, the Super Mushroom had an additional effect. Not only are the fighter's size and weight increased, but his/her attack strength also increases. An attack that normally does 15% damage could do near 30% damage when the fighter is a giant.

Trivia

 * The manual of the original Super Mario Bros. actually refers to the Super Mushroom as the "Magic Mushroom", but the name was changed due to the accidental reference of hallucinogenic mushrooms.
 * The Super Mushrooms in the Super Smash Bros. series look exactly like the ordinary mushrooms used in the most recent Mario games.