Katthveli
Katthveli (Cat-Whale) is one of the illhveli (evil whales) in Icelandic maritime folklore, a seal-whale hybrid with cat-like whiskers, hooked claws on flippers, and a terrifying scream. It aggressively attacks boats, ramming and capsizing them. Documented in Jón Árnason's collections and by 19th-century Icelandic naturalists.