In the Norse worldview, the phenomenon of shapechange encompasses various aspects.
The Norse word Ham·r means ‘skin’ (including a pelt, hide, leather or fur), and by extension means the ‘shape’ of a creature that is in this skin.
In the context of Norse animism, this ‘shape’ is a technical term for the shape of a ‘mind’ (hugr), the mental experience of a form, an ‘identity’.
The person that is ‘shape powerful’ (Ham·rammr) has a strong mind that is able to achieve the following feats (in increasing order of difficulty).
• ‘Going of a Berserkr’ (Berserks·gangr), trancing into the mental identity of an animal, to exhibit savagery and strength.
• ‘Shape traveling’ (Ham·farir), sending ones mind out-of-body to manifest elsewhere in such a savage animal form.
• The mind is so strong the projected mental shape actually transmogrifies the physical body into the animal form.
Bodily shapechange is rare, and usually associates with nonhuman Jotnar/Troll, or so on, but certain humans did it or even did it to other humans against their will. Typically, references to ‘troll cattle’, ‘troll cats’, ‘dragons’, and so on, are various Jotnar taking animal ‘shape’, sometimes monstrously.
D&D 3e can equate the method of this ‘shape power’ with psionic psychometabolism. However, this savagery spooked the Norse. Almost all the ones who do it are monstrous, whether human antagonists or nonhuman monsters. Altho it is the persons own mind doing it, the shape travelers often lost their humanity during it. The Norse responded to the concept of shapeshifting perhaps similarly to way some Europeans might respond to the concept of demon possession.
Whether Norse, Aborigine, Amerindian, or so on, reallife prehistoric animism is roughly equivalent to D&D psionics. It is the power of the ‘mind’ (Hugr). All features of reality are interactive mental presences. If you can visualize it is a real experience to some degree. In Old Norse, the term for ‘mindforce’ in the sense of the power of ones mind to influence external reality, is literally called ‘minds’ (Hugar), as an irregular plural, conveying the sense of ones mind being everywhere to where ones thoughts can travel.
Altho Norse animism is decisively ‘psychic’ in nature, it often self-identifies with the wild features of their dangerous environment. It could be, the D&D ‘primal’ magic is explicitly the psionic capacities of nature itself.
Shamans (as a term for various cultures) are psychics. But they especially attune with mental presences of natural features. Humanity is one cosmic feature among many. Among the Norse, the only formal institution of a shaman is female, the Volva. Informally some men also demonstrate these psychic abilities. But farther north, among the Finnar (equivalent to the Sami today) the shamans tend to be male.
