So there are shape-changing cults in the Dawnlands, and I model them using Mysticism from Mythras. They're most commonly found amongst the plains nomads - the Jarushim and Kadiz - where they are cross-clan associations of hunters and herders. Eagle, bear and coyote are the most common male shapechanging lodges, and crane, snow leopard and deer being the most common women's lodges.
Here's the talent list for the Coyote Runners, one of the more common male shapechanging lodges:
Enhance Healing Rate
Enhance Movement Rate
Formidable Natural Weapons
So this necessitated creating a Shapeshift trait. I'm using some of the information drawn from the shapeshifting spirits in the Animism chapter of Mythras (pg. 152).
In the Dawnlands, the mystic must be wearing a cloak made from the skin, feathers, fur, scales, etc. of whatever the creature they want to shapeshift into is, and they must hunt the creature and make the cloak themselves. They also can learn a "Beastform" combat style (common to all forms) that gives proficiency with Unarmed and Natural Weapons, and comes with Unarmed Prowess as a combat trait.
Shapeshifting is associated with a specific animal form - it's always Shapeshift (Coyote) or Shapeshift (Bear), etc., allowing access only to that animal form, rather than shapeshifting into any animal whatsoever. The mystic gains the average physical characteristics, armour points, hit points, creature abilities, and locomotion types of the animal when they shapechange, but keeps their own skills.
Unlike other traits, Shapeshift has variable intensity (similar to augmentations), costing 1 Magic Point per point of intensity. The mystic must maintain the trait with a minimum intensity equal to the intensity of a shapeshifting spirit able to transform them into that animal, as per page 152.
e.g. Transforming into a giant lizard requires a minimum intensity of 2, since a giant lizard is SIZ 19, and one requires an intensity 2 shapeshifting to transform into creatures between SIZ 13 and 21.
However, each level of intensity beyond the minimum required that the shapeshifting mystic invokes allows them to increase the SIZ of the animal form by 3. The mystic's new form gains the benefits (increase hit points, damage modifer, etc.) of the increased SIZ.
e.g. If our lizard-transforming mystic were to maintain their shapeshift trait at intensity 4, the extra two levels of intensity could be spent to increase the SIZ of the giant lizard to 25 (3 per additional level of intensity beyond the minimum).
Wounds and fatigue are carried over between forms.
Shapeshifting's meant to be a capstone ability for mystics who are progressing through one of these totemic cults, so I'm pretty good with it being a strong trait.