Our third question comes from acelightning, who asked...
"How much Fae ancestry (by percentage) does a person need in order to have magic of their own?"
It's the merlins question! So:
If two fae of the same type have a child, the child is a pureblood. They are fully fae, and will inherit the magic inherent in their type of fae. Quentin is a pureblood, as is Tybalt.
If two fae of a different type have a child, the child is a mixed-blood. They are fully fae, and how well they will be treated is somewhat determined by how noble they are. Their magic will be a mixture of their parents'. January was a mixed-blood. Dean is a mixed-blood.
If one fae parent and one human parent have a child, the child is a changeling. They will inherit magic only through their fae parent. Most will be weaker than their fae parent. October is a changeling, as was Chelsea.
If a changeling parent and a human parent have a child, the child is a thin-blooded changeling. They may or may not inherit any clear magical talents from their fae parent. Some will look sufficiently human as to not need illusions, or be offered the Changeling's Choice. Gillian was a thin-blooded changeling. The polite term for them is "quarter-bloods," but "weak-bloods" is more common.
A thin-blooded changeling who does show signs of magic will still be showing it within the "tree" of their fae ancestor. So if Gillian had any magical talents, they would have been things like minor illusions and detecting medical conditions through the taste of blood (not that she had any reason to go around drinking people's blood).
It's in the next generation where things get interesting.
A person with one-eighth fae blood or less is not considered a changeling: they will not face the Choice, they will die of old age (although it may take a long time), their flesh will decay when they do die. The night-haunts will not come for them. Most will have no magical talents at all. One in ten, however, will be the equivalent of Chelsea: they will have stronger magic than anyone expects. And they will have no innate restrictions. Iron doesn't burn them; oaths don't bind them; and most of all, their magic is formless. They get no starting talents or weaknesses.
All their magic will be of the sort Toby calls "hedge magic," using ingredients and rituals to get the desired effect. They are, essentially, wizards, using their natural talents and the rituals of trial and error to bend the world to their will. Or, as they are called by the fae, merlins.
Merlins usually manifest between one-eighth and one-sixteenth fae descent, but once it's in the line, it's there forever. Someone with a fae parent twenty generations back could, potentially, turn up as a merlin. There aren't many of them left these days, and those that exist rarely learn what they can do. They were one of the costs of the fae/human conflicts, since it left them without teachers.
Merlins are wild cards. Most consider them not to be trusted.