Barkskin

When the druid casts the barkskin spell upon a creature, its armor class improves 1 place because the creature’s skin becomes as tough as bark. (Armor rating does not change.) 

In addition, saving throws versus all attack forms except magic increase by +1. This spell can be placed on the druid casting it or on any other creature he or she touches. 

In addition to mistletoe, the caster must have a handful of bark from an oak as the material component of the spell.