The Madwitch

The Madwitch is a famous figure in stories and rumours throughout the Sealands —everyone who grew up in Malfa or the Forges, at least, will recognise the name. She is supposedly an ancient sorceress who lives within the fey doors—neither here nor there, but in-between places. She might be of fey origin, or she might once have been a mortal creature who dabbled in the Wrong Magics.
Visiting the Madwitch in stories has a fairy-tale quality; if you can find her, you can ask her for a favour, and she will always give it to you—but you might not like what you get. She will also ask a favour of you in return, which might be absurdly mundane, or might lead to your death or enslavement.
What exactly is mad about the Madwitch varies with the stories. Sometimes she is described as disturbingly irrational, like a living dream; sometimes she is portrayed as being in a permanent towering rage, due to some deadly insult in her past.
In most stories, there is nothing in particular tying the Madwitch to the Maveren, but sometimes they will be associated somehow, in some antagonistic way—as though the Madwitch is one of the Maveren's long-standing opponents. Sometimes the Madwitch is identified as one of the The Three Undying Enemies of the Maveren, but that is usually considered to be a children's story with no basis in fact. She is sometimes also equated with the Queen of the Green Court, the ruler of the Feywild, but this too is not taken very seriously. No Maveren knows anything about the Madwitch, except the stories they too heard in childhood.