The Cwnn Annwn (roughly pronounced "coon ann-win") are a left-handed Legacy that are dedicated to creating an ideal plane without the fear of Paradox and the lingering threat of the Abyss. To this end, they have bouded themselves to thaumavorous beings of the Lower Depths that aid them in their quest in exchange for Mana.
Originating in Wales, the Cwnn Annwn are a relatively new Legacy, having formed after a young mage under the shadow name of Argent had claimed that Ascension was impossible and humanity should seek another realm to conquer. After being banned from his local Consilium for his heretical beliefs, the mage used a ritual to banish all the Mana of a Hallow he had tainted with sacrifice into the Depths, where he found out that he could create phantasms from his will alone and as such created Annwn, the Garden, a beautiful paradise free of the threats of the Fallen World. The only problem with it is that Annwn is inherently unstable and requires vast amounts of Mana to avoid breaking up and being absorbed by the rest of the Lower Depths. The void it was built in is also far from being uninhabited. Every member of the Legacy is host to a being of the Lower Depths called a Hound of Annwn, an invisible force that lacks any of the Arcana and so is extremely difficult to perceive with magic. After shaping their souls according to their attainments, every mage of the Cwnn Annwn gains a Hound as a familiar. The Cwn Annwn have found that, with effort, they can force their hound to rebuild a facsimile of what they destroy within Annwn, which gives them some measure of control over what is sacrificed to power their realm. Their paradise is built from these stolen patterns — when a Gardener finds something worthy of inclusion in Annwn, he directs his Hound to reduce it to Mana and the image of it appears within the realm.