Spirit Form
The shaman slips into a space between the spirit world and the material plane, rendering them partially incorporeal. For the next 5 rounds, all physical attacks directed against the shaman deal 50% of their normal damage. During this time, the shaman is also under the effects of Improved Invisibility and cannot be directly targeted by spells. This invisibility is not of the Illusionary protections type.
This effect is similar to Shadowdancer's Shadow Form. It's a high-level class ability that can be selected multiple times.