Grissoul was the seer for the Juskarath tribe, and was an elderly vixen with a bad, twitchy eye. She wore a painted barkcloth cloak and bracelets of coral, silver and brass, as well as the traditional tattoos of the Juskarath clan. Grissoul had many pouches and bones attached to her belt, as well as other seer's paraphernalia. She rather eerily foretold many events, such as the Taggerung being the death of Sawney Rath, and the fact that the Taggerung would come from Redwall Abbey. She was partial to dove eggs.
Grissoul also gave some useful advice to Antigra and her son Gruven, who were planning to take over the clan. During their conversations, she revealed to them that she believed that her life's mission was to stop the Juskarath being torn apart by strife, even if it meant bending the truth of her omens a little and changing loyalties when necessary. This held true when Antigra later slew Sawney - to please Antigra and keep the tribe from falling into disarray, Grissoul publicly pretended to summon Sawney Rath's spirit, which "selected" Gruven as the new cheiftain.
When the Juskarath were defeated and incorporated into the Juskabor Clan, Grissoul was taken in by the clan cheiftain Ruggan Bor. She found favor with him as a second seer, working together with his own vixen Ermath (who became slightly jealous). After Grissoul predicted that Ruggan Bor would be defeated at Redwall Abbey's gates, she suddenly died of old age, still sitting upright by her fire. Ermath was shocked at her sudden death, but Ruggan pointed out that she had been a truly ancient beast, liable to pass away at any time.
Bizarrely enough, Grissoul predicted Ruggan Bor's ascension to Taggerung; he killed Antigra, who had overthrown and slain Sawney Rath. Grissoul had earlier foreseen that whoever slew Rath's murderer would be the Taggerung; however, nobeast save she knew that Antigra was really the one who slew Sawney Rath, for the Juska had been tricked into believing Tagg had done the deed.
- She is the only villain known definitely to have died of old age.
- Her name may be derived from Gris, the Latin word for the color grey.