9. Daggermouth (Season 3, Episode 10)
According to Seamus, Daggermouth was a giant fish (nay, a "sea monster") to be feared by all seaside dwellers, as it once killed a fisherman by the name of Salty.
When a $50,000 bounty went up to capture the creature in "A Fish Out of Water," Peter Griffin was warned to be careful around, if not completely avoid, the carnivorous bluefish before his arduous quest to discover it with his friends.
Of course, it wouldn't have been an episode of Family Guy if Daggermouth simply turned out to be a man-eating fish. Instead, the dreaded monster was actually a whimsical robot created by no other than the "deceased" sailor Salty. It was intended to serve as a marketing device to generate some extra merchandise money.
"A Fish Out of Water" went on to be the only time the showrunners made good use of Daggermouth, and Peter was paid to keep his mouth shut about what he witnessed, an offer he was more than happy to accept. Afterward, the fish was seen on Peter's bedroom TV during a clip from a fictional Nickelodeon cartoon called Daggermouth and Boom Boom. Still, ever since, he has dropped off the radar.