Sister Nil appeared in about a dozen issues of the mid-'90s Doctor Strange run. She was a lilin/daughter of Lilith who at first tried to attack Strange but got captured and bound by him. She wound up turning good and eventually Strange gave Nil her freedom (it's actually the storyline where he becomes a long haired younger guy), and then she gets 1 more appearance and that's it. She hasn't appeared in a comic since like 1995.

Which is insane because you would think that cute pale-skinned/goth looking succubus with a naive curiosity about humans and an, again, somewhat childish crush on Strange would be a fucking goldmine in our current goth and kawaii obsessed era.