Kraken

"Any idea when Jones will release said terrible beastie?" - Jack Sparrow

Terror of the Seas
The Krarken was an enormous sea creature, very closely resembling a giant squid. It is summoned by a giant hammer aboard The Flying Dutchman. The Kraken is twice as large as a normal ship with tentacles as thick as a main mast, and as long or longer than one. The beast is sent after whoever owes Davy Jones something (namely their soul), and cannot be stopped untill it achieves its goal.