Poison Mushroom

A Poison Mushroom (or Poison Shroom) is a Mushroom that powers down or defeats Mario or Luigi if they touch it. They have the opposite effects a Super Mushroom may have. They first appeared in the Japan-only game, Super Mario Bros.: The Lost Levels. Currently, they appear now and then, hindering the player.

Super Mario Bros.: The Lost Levels
In Super Mario Bros.: The Lost Levels, a Poison Mushroom will defeat Small Mario or Luigi, or revert Super or Fire forms into small but they have no effect on the Invincible form. They are found in Brick Blocks and ? Blocks, coming in many different colors in the original FDS game. In the remake of Super Mario Bros.: The Lost Levels, Poison Mushrooms changed their main appearance to blue.

Donkey Kong
Poison Mushrooms were featured in Donkey Kong. Sometimes, Donkey Kong or Donkey Kong Jr. would throw them at Mario, and sometimes they were contained inside barrels. Whenever Mario comes in contact with one of them, it will cause him to briefly shrink in size, disabling some of his abilities in the process (the ability to swim, climb ladders, etc.). After a few seconds, Mario grows back to his regular size.

Super Mario Kart
Poison Mushrooms were also featured in Super Mario Kart as items, however they were only used by the computer-controlled drivers Princess Peach and Toad, and not usable by the player. If a player drove into a Poison Mushroom, they would become small, ending up moving slow and vulnerable to other karts in the area, as they could end up squashed if run over by a full-sized kart. An interesting feature of the Poison Mushroom in Super Mario Kart is the fact the player can also become big again if they run into another Poison Mushroom; this also works if the player were made small from a Thunderbolt by the other player (as CPU players cannot use a Thunderbolt in this game).

Mario Party
In Mario Party, when landing on a Mushroom Space, if the player chooses the Poison Mushroom, they will lose their next turn.

Mario Party 3
In Mario Party 3, the Poison Mushroom is an item that the players can use on either themselves or one of their opponents. A player who is cursed by a Poison Mushroom can only roll the numbers 1-3 on their next turn. It is possible to eliminate the curse by using another Mushroom or a Magic Lamp. It is Waluigi's favorite item.

Luigi's Mansion
In Luigi's Mansion there are Poison Mushrooms that bosses throw when Luigi tries to suck them up. They make Luigi small and lose pearls and coins, also making them escape as Luigi is too tiny to suck up anything bigger than a lost pearl. Also, if Luigi calls for Mario by pressing the A button, his voice can barely be heard.

Mario & Luigi: Superstar Saga
In Mario & Luigi: Superstar Saga, One of the things Trunkle can suck in his mouth during the "Envelop and Heal" move is a Poison Shroom. They are colored the same, and Poison a brother if touched. Popple sometimes throws them during his, "Throw from the Bag" move. They are also the same, but the poison they give a brother if touched is more severe. When the bros. travel to Little Fungitown, Mario eats an Invincishroom, a mix of a Starman and a 1-Up Mushroom. However, Mario, being an outsider, was not immune to the dubious concoction and fell gravely ill. This Invincishroom was, to Mario, like a Poison Mushroom.

Super Smash Bros. Melee
Darker red Poison Mushrooms, with sinister eyes were later seen in Super Smash Bros. Melee, in which it temporarily shrinks characters down to one-fourth their original size. That makes the player smaller, but also makes him/her easier to KO.

Super Smash Bros. Brawl
In Super Smash Bros. Brawl, Poison Mushrooms had another side effect. Not only does the fighter become smaller and lighter, but his/her attack power drops greatly as well. An attack with strong knockback would pack less power than normal when the fighter is tiny.

Paper Mario: The Thousand-Year Door
The mushroom was seen once again in Paper Mario: The Thousand-Year Door. Poison Shrooms could be created by Zess T. by mixing a Slow Shroom and Inky Sauce / Point Swap or Trial Stew and a Dried Bouquet. If Mario or his partner eat this mushroom, the user will lose half his HP and be poisoned. Strangely, in battle, there is a small chance that when eaten, the Poison Shroom won't poison its user, but will restore all HP instead. There is a common misconception that the Feeling Fine badge(s) are required for this to happen - this is not true; it is simply a random occurrence. They're one of the pictures that the player can earn when in battle. If three in a row appear Mario's HP, FP and SP will all be cut in half and all of the audience members will leave.

Ghost T. also died because he ate a Poison Shroom on the Excess Express.

Super Paper Mario
In Super Paper Mario, Poison Shrooms are a much more common occurrence than in its predecessor, occasionally being dropped by Zombie Shrooms, Cursyas, and their relatives. They are used slightly more in recipes; for example, a single Poison Shroom can produce a Dangerous Delight. In addition, any recipe that requires a Poison Shroom can be cooked using a Ghost Shroom instead, if Poison Shrooms are in short supply (Ghost Shrooms can be bought from various shops, or obtained via Merlee's charms).

Trivia

 * The Poison Shrooms on the Paper Mario: The Thousand-Year Door's slots have faces, but the Poison Shroom item doesn't.
 * It was erroneously stated in Super Smash Bros. Melee that Poison Mushrooms first appeared in Super Mario All-Stars, when in actuality they first appeared in Super Mario Bros. 2 (Japanese Version). This was corrected in Super Smash Bros. Brawl.
 * The reason for this may likely be due to the fact that Super Mario Bros. 2 (Japan) was never released for the NES. However, despite this fact, several characters from Japan-only titles did appear as trophies in the North American version of the game.