Stormfin was a giant male pike used by Mossflower otters to battle and kill the Gloomer. He was captured by Mask and Skipper Warthorn, and imprisoned in a stretch of the River Moss known as Camp Willow.
Skipper kept Stormfin in a small channel by a sluice gate his otters had constructed, and unleashed him whenever they needed the fish to fight. When the otters in the river heard the banging noise from a log they knew to get out of the water. Skipper claimed the Stormfin would always return because it knew there was food in its small channel.