Casual Viking |
"This ability uses the same rules as the wizard's arcane bond class feature and is treated as a familiar, except as noted below."
"1) A shaman uses her level as her effective wizard level when determining the abilities of her spirit animal. A shaman can select any familiar available to wizards to serve as her spirit animal, although her spirit animal is augmented by the power of her chosen spirit.
2) Once selected, the spirit animal cannot be changed.
3)Although a shaman's spirit animal uses the statistics of a specific animal, it is treated as an outsider with the native subtype for the purposes of spells and abilities that affect it."
2) is the reason Improved Familiar doesn't work for shamans, but almost everything else should be fine.