Water Entity

The Water Entity was a powerful artefact created by Xagor in Final Fantasy Legend III, it resembled a gigantic urn atop a floating cloud and continually spewed out water by which to flood the world and via unknown magic spawn monsters that proceeded to infest the world: as time progressed the Water Entity had flooded almost the entire world and made life intolerable for humans - this prompts the heroes of the story to go on a time-travelling adventure to find a means to defeat the Water Entity, along the way they would discover the truth about its origins.

The Water Entity was ultimately destroyed by a dying Sol as his final act - with its destruction the mass flooding of the world was undone and the monsters stopped invading, the Water Entity itself was not a sentient being but rather a mystical construct and was never actually faced in battle during the game (though its creator was).