An eidolon is a specific and powerful type of companioncreature that is bound to a Summoner, often extraplanar or monstrous in nature. The Eidolons are believed to temporarily return to their ‘home plane’ whenever desummoned, though this has not been confirmed and many questions have been raised what could constitute as a home plane to many types of Eidolons (for example, where do animal-like eidolons go?).