The item that makes a character larger and stronger in Super Smash Bros. is the Super Mushroom.
Borrowed from the Mario series, the Super Mushroom temporarily enlarges a fighter and increases their power. In Smash, its effect is immediately recognizable: the character becomes giant, making attacks more imposing and often changing the feel of the battle for a short period. It is one of the series' many crossover items that adapt a familiar franchise power-up to platform fighting.
The Super Mushroom originated in Super Mario Bros., where it changed small Mario into his larger “Super” form and allowed him to withstand one hit. It is easy to confuse it with the Poison Mushroom, which harms or weakens a character, or with the Super Star, which grants temporary invincibility. The Hammer and Star Rod are also powerful Smash items, but they do not enlarge the fighter.