Grendel is the cat of the Deadly Nightshade Gardening Club's Chairwitch, Archaniz. He looks exactly as a witche's cat should, with night-black fur and yellow eyes. Morwen finds him an idiot, and has told Archaniz multiple times to to bring him when she comes to visit, but "nine times out of ten she doesn't listen". Morwen's cats don't seem to like him either. He gets chased by the cats, when he runs over the hill, screaming about some rabbit (actually Killer). The cats think that a cat who's scared of a rabbit is more than stupid. Grendel also appears to have a bad temper, and Morwen's cats say that he eats too much.

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