Slimnah was a Sluagh, played by Jamie.
Background
Slimnah (generally called Slim) formerly lived in the basement of Lady Catherine's house, and was rarely seen until recently. His background is not common knowledge. Slim quickly gained something of a reputation for giving useless answers to questions asked of him, and for asking strange questions in return. He was generally distrusted; he seemed to be on best terms with Jellybean.
On Lady Catherine's Sain Day Slim was appointed Seer of Waldren House. By the end of that year he had betrayed Lady Catherine, allowing a Sluagh to live in her head, and left Waldren House. On the occasion of his farewell, he gifted Jacoby with the death of Madame Rain, which caused some trouble.
Physical Description
Slim appears as a boy of about ten years old, thin and pale. He dresses in robes of deep purple and streaks of black and silver, with a head scarf covering all but his face. These robes are thick and full, and reach well down to the ground. His nose and mouth are undeveloped, his dark eyes large and round. His teeth are small and pointed, as if filed down into sharp triangles. His hands, the only other part of him visible, are long and thin.
Slim speaks in a whisper, always, and even when sitting or standing, he squirms his body and head at odd angles. He has the unpleasant habit of licking his fingers and hands. In conversation, however, Slim tends to politeness, in form if not in content.
Faerie Form
Few differences are apparent between Slim's faerie form and his mortal seeming. He is slimmer, paler, and his eyes are sunk further into his skull. He lacks any traces of teeth. There is a smell of rotting leaves. His physical mannerisms are even more extreme in this guise: his body twists impossibly, and his hands constantly glisten with moisture.
His robes are in fact a Midnight Cloak, a garment of considerable power, though it is openly distinguished from his mortal clothes only by the fact that the patterns of purple and black move slowly. Slim used the cloak to leave Waldren House, by tossing the back of it over his head - as the cloak fell over him, both cloak and Sluagh disappeared.