Boon of the Old Faith

For Archdruids, the call of living beings hold inherent value, and the entities beloved by the ancient druidic traditions can hold a special call. Upon reaching the status of Archdruid (20 consecutive levels in Druid), a druid can begin to hear the call of other living entities beyond beasts, and transform into one additional type of monster, with the same CR limitations as their normal wild shape.

For example, an Archdruid from the Circle of Spores may be able to turn into an ooze, or an Archdruid from the Circle of Land may be able to turn into a plant.