Poison is a hazard, present only in Pikmin 2 and Hey! Pikmin. It takes the form of a gas, colored purple, and is fatal to Pikmin that are not White or Bulbmin – they will begin choking if the top of their stem is covered in poison gas. Choking Pikmin will run around in a panic and, if not saved, will eventually succumb and die. These Pikmin can be rescued by being whistled at.
Poison gas is completely harmless to leaders, presumably because their spacesuits filter the air. However, the poison emitted by the Comedy Bomb the Titan Dweevil wields can damage and knock leaders down.
Poison is less prevalent and a bit different in Hey! Pikmin, however. It only appears in the final sectors, the Lushlife Murk and The Final Stretch, and mostly takes the on the form of poisonous lakes and attacks from the final boss. Any Pikmin that falls in, or even Olimar himself, will instantly die. Poison geysers also appear exclusively in the Burning Bog, and they also kill Pikmin immediately, despite only harming Olimar. Since there are no White Pikmin in this game, poison must be avoided with careful movements and timing.
Poison gas does not appear by itself, but is rather emitted from a few sources.
One of the White Pikmin's most notable traits is their relation to poison. They can withstand poisonous gas without choking, making them ideal to destroy poison sources. In addition, the White Pikmin themselves are poisonous – if an enemy ingests one, they will instantly receive some damage, and some purple particles will flow out of them, similar to the ones released from poison gas.
In other games
Poison gas is absent in Pikmin, although the Smoky Progg releases some element that instantly kills Pikmin caught by it. Although never confirmed, some fans just call the element "poison".
Poison may have meant to feature in Pikmin 3, as a poison geyser can be found in the files, and White Pikmin do return in Pikmin 3, albeit only in Mission Mode and Bingo Battle. If the Poison geysers are hacked in, White Pikmin are the only Pikmin which are immune to them. White Pikmin do not exhibit any special resistance towards any other element in the game.
There are other effects in the game which many have interpreted as poison, but are not. The Vehemoth Phosbat releases a cloud of purple dust, resembling poison gas from Pikmin 2. The effects of this gas are similar, in that the dust makes the affected Pikmin start choking and run around in a frenzy, and can be removed with a blow of the whistle. Likewise, the Toady Bloyster and the Sputtlefish can emit clouds of ink which have identical effects. The key differences between these effects and poison, are that they do not result in death, fade away after some time, and White Pikmin are just as susceptible to the effects if hacked or glitched into position. Therefore these effects are less like poison, and simply cause a panic.
Super Smash Bros. series
In the Super Smash Bros. series, poison is a thematic element to the properties of White Pikmin, causing their latch attack and grabbing attack to deal much more damage than other Pikmin types. This is represented by the darkness effect, which causes opponents to emit dark purple energy when damaged.