Ceto

"Pray you never have to face her. She is the most powerful Sea Monster ever, Ceto."

           -Chiron speaking of Ceto

Ceto, (Cetus or Keto)- is the most powerful sea monster of Greek mythology and the second most powerful monster of any type, falling only behind the storm monster Typhon.

[http://The Stolen Trident The Stolen Trident]
Ceto was the monster guarding Poseidon's tident in Tampa Bay,FL. Because of the strong aura produced by Ceto, the tridents power was hidden. Cetos aura also hid the location of the lost city of Atlantis, which turned out to be under the brand new SeaWorld. Ceto was slayed by Connor Anderson.