Umibōzu

was used by Amachi to terrorize the Land of the Sea.

Abilities
Umibōzu itself is nothing more than water that has been gathered and held together by chakra, making it virtually indestructible unless it is completely evaporated. It's main attack method is capturing targets in its water body and drowning them, as well as shooting powerful bullets of condensed water at its opponents.

Land of the Sea Arc
Naruto Uzumaki got swallowed by its indestructible water mass and was completely immobilized, until he gained a burst of chakra from the Nine-Tailed Demon Fox and eventually broke free, shattering it into tiny droplets. During a later encounter, after Umibōzu reformed, Naruto resorted to summoning Gamabunta and it was defeated by Naruto throwing an exploding tag attached to a kunai into Gamabunta's oil, completely evaporating it.