Amanita muscaria was a fungus native to the subarctic climates of Earth. It was poisonous, and ingesting it could cause profuse sweating, convulsions, and acute delirium. The Vikings knew it as the atuta, a powerful plant they boiled into broth and consumed before battle for spirit.
Amanita muscaria is known in English as the fly agaric or the fly mushroom. There is a common notion that Vikings used it to to induce their "berserker" rages, but there is little historical evidence for this.