Personally, I was at one point going go write a breakthrough that used the warping reactions of the Folk Witches and Gruagach as insight.
It was going to be a method of transforming your warping points into physical and supernatural flaws by channeling the supernatural taint into specific parts of your body and burning it off in a change to your nature.
The mechanics would be something like-
This is a Rego Vim lab activity. During this activity, form a transformation total:
(Stress die + Warping Score)
At the end of the season, the magus loses points of warping equal to their transformation total. If they lose less than ten points of warping, they gain a general or supernatural minor flaw. If they lose more, they instead gain a major general or supernatural flaw.
The flaw gained should represent the body of the magi becoming more inhuman or obviously supernatural, or be a general flaw that reflects a new way their behavior is being influenced by this supernatural taint.
Magi who know this technique always have a pattern to their transformation. The player decides what, exactly, their magi is becoming (though the magi has no such choice). They may be transforming into a huge human-faced bird, a heartless faerie queen or similar.
The magi's lab total reflects how well controlled the transformation is. For every five points of her lab total, or fraction thereof, the magi gains a poinf of safe transformation. If the magi's transformation total is equal to or lower than these points, the player or the character decides what flaw is gained. They may also reduce the number of warping points lost, to allow a lesser flaw to be gained, if they wish.
If the transformation total exceeds this amount, the transformation is out of control. The story guide picks the flaw gained. Additionally, they may choose to grant the magus another temporary flaw of the same magnitude. Any flaws chosen by the storyguide must still conform to the pattern of warping for the magi, as defined by the player. Temporary flaws either vanish after a year (as the hermetic duration) or after a suitably dramatic moment involving the story flaws of another character in which the magi resolves to cling to their remaining humanity.