The Super Mushroom appears on the stage and keeps sliding to the right. In Melee, it will slide left if it spawns on the right half of the stage. A character touching it will grow larger, with the following effects:
The transformation lasts about ten seconds. Touching a Super Mushroom while under the effect of a Poison Mushroom and vice versa will restore a character to their normal size.
The Super Mushroom does not appear in the game. Giant Donkey Kong, who has the effect of the Super Mushroom, is an opponent in the 6th stage of the 1P Game mode. The Super Mushroom also cameos as the Universe symbol of the Mario universe.
The Super Mushroom made its debut in the Super Smash Bros. series in Melee, with the effects described above. Additionally, in the Special mode Giant Melee all the players are permanently under the effect of a Super Mushroom. Giant battles can also occur in Classic Mode.
Super Mario Bros. veterans will recognize these power-ups, which hid inside brick blocks and helped Mario and Luigi withstand enemy attacks. In Super Smash Bros. Melee, they temporarily turn your character into a giant. Not only will your size and strength increase, but so will your mass, making it harder for foes to knock you off.
In Super Smash Bros Brawl, characters strike a pose while growing/shrinking, briefly relishing their increased size and lamenting their return to normal size. Most of the items held by the player, as well as their own projectiles, will be proportionate to their bigger size. Certain attacks or charge ups can be interrupted if a Super Mushroom touches the player in the course of doing an action.
Giant battles also return as a Special Brawl feature and in Classic Mode.
Description from the Super Smash Bros. Brawl instruction booklet
Briefly boosts your size and power.
The Super Mushroom returns in Super Smash Bros. 4, keeping its prior behavior. Giant battles are once again available as a Special Smash option and during Classic Mode.
In Smash Tour
The Super Mushroom is a red trophy item: when selected, it makes the user start a battle under the effect of a Super Mushroom. Using this trophy cancels the effect of a Poison Mushroom trophy used by an opponent.
The Super Mushroom is one of the items that can appear during a Transformation Smash.
The Super Mushroom is an important aspect of the entire Mario series. Starting in Super Mario Bros., where it was originally called the Magic Mushroom, it made the user larger, allowing him to withstand hits from enemies. Since then, it has appeared in nearly every Mario sidescroller with the same effect, with the exception of Super Mario Bros. 2, where it simply increased the player's health. It has appeared so much in the Mario series that it is now considered an icon of it, and as a result it serves as its series symbol in the Smash games.