I actually have a player, who plays a half undine. I´m modelling merfolk more or less after the ancient greek origins and assume that they are some kind of independent fae court. Since we are playing in germany, more exactly Bremen, the fae of the north sea are an important force of the local supernatural politics. The player itself doesn´t really belong to this merfolk, since I thought of a darker breed of merfolk faeries, who life in the deep, cold reaches of the ocean, and who are some kind of cruel seers, who belong to the winter court.