Stay in one general area and hit all the platforms you can. Get under em and spam the up fire attack when he opens his mouth. Grab the sp from the platforms he destroys. Rinse repeat.

He has only 3 major attacks of note. If his mouth is charging up red, jump in the water and swim away to get far enough to avoid the stream of fireballs. If he charges yellow, get out of the water as he'll electrocute it. When he's doing his electric move it's also the best time to go under his chin and blast him with up fire attack like Zerofox said. When the serpent is diving in the water, watch the bubbles to see where he'll strike so he doesn't ram into you. That's really it, he's not that hard, having the charge cannon from the save point helps a lot so that you don't have to spend ninpo on shurikens to create platforms.