Red mushroom (InstanceClass, 10)

From Compile Worlds

A red mushroom will make you grow to double your height. As such, it's recommended not to eat them indoors.

Red mushrooms can often be found in question mark boxes.

In Mario RPGs, Mario is invulnerable to the height-doubling effects of these red mushrooms; instead, they heal him by 10 HP.

Red mushrooms also appear in the Mario Kart series, where they give you great speed boosts upon consumption instead of growing you. Sometimes, these come in three-packs called Triple Red mushrooms (Or typically, just Triple Mushrooms).

Finally, starting with Super Smash Bros. Melee, Red Mushrooms began to appear in the Smash Bros. Series, where they actually do what they normally do. Grown characters have additional benefits of being harder to knock of the stage, more launching power, and a deepened, manly voice.

In Minecraft, just to catch you out, red mushrooms hurt you, for 1.5 hearts of damage. Instead, you should eat brown mushrooms to heal you for 2.5 hearts.