Source: M. A. Lloyd
Shapechanging is a common theme in magical tales, and transformation into a totem animal is probably one of the oldest forms of magic. A Path is presented below, but it is also possible to increase the difficulty of these rituals and attach them to the Path of Health, or make them Mysteries. Don't overlook the possibility of using one of the GURPS wereform rules for magicians with only a few alternate forms. It's probably also possible to mix wereforms and Spirit Warrior - Totem Spirit sensibly, but I'm not sure how.
Changes the magician into his alternate form - a natural animal that reflects his inner nature. Select your altershape carefully, since you always transform into the same animal. The GM should allow any form that is not clearly at odds with the character description (dangerous carnivores are not appropriate for vegetarian pacifists for example). The effect lasts until the ritual is repeated; both shapes are the magician's natural form. The magician retains his intelligence, and in some forms (birds in particular) may still be able to speak. He can use the basic natural abilities of the form, but complicated aerobatics or tearing things apart with your teeth take practice (and purchased skills) to master just as Acrobatics or Brawling do in human form.
The appearance of the target alters to reflect their inner nature. Only appearance level changes, the target remains recognizable. The GM will need to judge the inner nature of the target carefully to rule on his final appearance. Most people will be Attractive, those with serious character flaws or questionable morals (like say the vast majority of PCs) end up Average. Only the purest of motives merit Very Beautiful, and only the blackest of villains should drop to Ugly or worse. Anybody so far gone as to merit Monstrous probably considers it a positive effect; he fits in better in Hell. Outer appearance may already match inner form, in which case nothing observable will happen. This ritual can be resisted and can count as a hostile ritual with a backfire risk.
Allows the magician to transform a willing target into any natural animal, plant or object of similar size - be generous, anything from a mouse to a horse should be OK. The target can return to natural form early by making a Will roll (one try per turn).
Changes the target into an animal of the magician's choice. It may not change the victim into a form that cannot survive in the current environment, nor shorten his life, even if the form naturally ages faster. The victim retains his intelligence, and often even his voice. The Mystery may even stabilize his sanity, spending a century as a toad never seems to drive the victim mad in fairy tale sources of this spell. Like Enchanted Sleep, early termination options can be added if the magician desires, otherwise use the normal duration. In most tales this is cast by incredibly powerful beings who can take the penalties for fast casting something with a thousand year duration.
Variants that change the target into trees, objects, or stone or metal statues work similarly - though they usually prevent speech and may leave the target unaware of his surroundings.