Big Lenny

Big Lenny is the biggest, baddest, meanest and scariest jellyfish of them all. Local jellyfishers are afraid of Big Lenny. As SpongeBob revealed in I'm Your Biggest Fanatic, Dr. Manowar is the only person who has survived an attack by Big Lenny, getting by only with a huge bump that hurts when touched. This implies that Big Lenny has stung, and thus killed, numerous other Jellyfishing enthusiasts. He only appears in episode "I'm your biggest fanatic"