How (visibly) obvious is the typical Twilight Scar?
I imagine Twilight scars can get a bit extreme when botching MuCo or MuAn spells, especially shape changing spells.
But if a Twilight Scar becomes part of a character's Essential Nature, does that mean it can be inherited by children?
ADDENDA in the case of magi who get Twilight scars while still capable of (and inclined to) have children. That is pre LP.
Presumably a non-zero number. Thank you master Itzhak
Keep in mind that most Magi who suffer Twilight Scars are likely older Magi, and once they have taken the Longevity Ritual, they're incapable of having children.
I don't think twilight scars are part of your human nature, so they wouldn't typically be inherited by your children. Children of warped people aren't generally warped, and you don't get scars without being warped.
But some scars might affect your reproductive capacity, and hence what your children are like.
I would take quite the opposite view. All of a magician's magic becomes part of his being, and any children he may have late in life may well carry the mark of it. So the child of a Flambeau mighty in the Arts of Creo and Ignem might have the power (or curse) to make stuff spontaneously self-combust, or perhaps have burning blood that is a source of Ignem vis. That of a Criamon might gifted with Intuition, Premonitions, or feel just weird. That of a Bjornaer might have animal features, or Animal Ken. And so on. But I would not have the individual scars inherited.
It is probably superfluous to point out that a Twilight Scar, despite the name, is not necessarily on a magus' body. Two Twilight Scars of Philippus Niger (GotF, p.59) are that "he can always tell
true gold from false" and "only male children are born at a place he has lived for more than a year".
I don't think that Twilight scars are inheritable - Twilight scars arise because of your Gift, and the Gift is famously not inherited. As always, whatever makes for the better story in your saga is probably the way to go.