As Legend says, the mountain peaks of the Pyrenees are the spine of the Serpent SuGarr, the Great Wyrm of the Pyrenees
For those who know it, the Mountain Wilderness Lore of the Pyrenees opens you up to many paths. It is how Antonio became a spell master, and it is how Rodrigo discovered his Latent Magic and transformed it into the Gift.
But it always carries a price.
On this path, lies the spirit of the Terragon Mist. It will demand of you a sacrifice and send you on a quest. The first fruit is that you will learn to take on shapes similar to your own.
Sigmundo alluded that this is how he learned to shapechange. Maurice used it and can now take human form (and a housecat shape too).