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. They are found in bricks, ? blocks, and hidden blocks, coming in many different colours in the original FDS game. The Poison Mushroom found in Super Mario Bros.: The Lost Levels was inspired by the poison Alice drank that made her shrink in "Alice in Wonderland".

Donkey Kong
Poison Mushrooms were featured quite prominently 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.

Mario Party
In Mario Party, when landing on a Mushroom space, if chosen the Poison Mushroom, he/she will lose his/her 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 elimate 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, Mario ingested a Poison Mushroom that was dark green with dark red spots in Little Fungitown. The mushroom made Mario extremely ill, forcing Luigi to journey to Guffawha Ruins to find the only known cure, Crabbie Grass. That was actually a mix of Starmen and Mushrooms, called the Invincishroom. Also, 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.

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 Mushrooms could be created by Zess T. by mixing a Slow Shroom and Inky Sauce 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, if the player or the partner have a Feeling Fine badge on, there is a small chance that when eaten, the Poison Mushroom will restore  all HP. 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 since he ate a poision shroom on the Excess Express.

Super Paper Mario
In Super Paper Mario, Poison Mushrooms are a much more common occurance than in its prequel, 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.

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.
 * In Paper Mario:The Thousand-Year Door, Poison Mushrooms are equivelant to actual poison in the real world, because Ghost T. died from getting poisoned by one of them.