Mushroom Pikmin
Mushroom Pikmin also known as Zombie Pikmin or Toadmin, they are Pikmin that are under the control of a Puffstool. The spores of a Puffstool cause Pikmin to be morphed into to strange form, also known as their zombification. These Pikmin are purple, have a black mouth with white pupiless eyes, and an orange mushroom on its head rather than a flower, bud, or leaf. These Pikmin follow Captain Olimar and attack him until he shakes them off or until he loses all of his health. If Captin Olimar is not being attacked, you can usally find them dancing around the Puffstool. Mushroom Pikmin will eventuallty turn back into their normal forms in a moment of time. These Pikmin will also fight other Pikmin, this will just decrease your Pikmin population.There was a rumor going around GameFAQs about a glitch where somebody had four Pikmin get zombified and two turned white and attacked the Puffstool and didn't turn back to normal until they entered the onion.This is a common thing on challenge mode, but it is unknown how the glitch occures.
http://img80.imageshack.us/img80/3096/whitemushroompikmincr7.png. A single white mushroom pikmin attacks a Puffstool