Metamorph

The material below is Open Game Content from a 3PP Source

Metamorph (Ex): An eidolon can change its base form as a full-round action. It changes all its starting statistics to match the new form, loses any free evolutions from its previous base form, and gains the free evolutions of its new base form. If it has any evolutions that are not allowed by its new base form, they cease functioning until the eidolon changes form again. If it gains a free evolution that it has bought already, the free evolution is lost until it changes form again. (A player should prepare in advance statistics for any form she wishes her eidolon to take—changing base scores, saving throws, and evolutions take awhile.)