Beastlands

Of all the planes, this one has no settlements, towns, citadels, or any other structures built by its petitioners. This is because upon arriving in the Beastlands, petitioners are transformed by great animal spirts into animals. They keep their skills, mental faculties, memories, and ability to talk. Additionally, whenever a visitor slays a beast native to the plane, the slayer must succeed on a DC 10 Charisma saving throw or become transformed (as the polymorph spell) into the type of beast that was slain. In this form, the creature retains its intelligence and ability to speak. At the eand of each long rest, the polymorphed creature can repeat the saving throw. On a successful saving throw, the creature returns to its turn form. After three failed saving throws, the transformation can be undone only by a remove curse spell or similar magic.

Because of this plane’s “perfect wilderness,” all creatures have advantage on survival, perception, and animal handling checks. Additionally, spells creating or controlling weather automatically fail. Furthermore, the animals of the Beastlands can’t be affected by spells that affect or control their emotions (such as animal friendship).