Siren / Mer, Trident

the trident can be equipped and can shoot with water bolts and can melee, and allows you to breathe under water, you should be able to buy it from the mer shrines with reputation (returning the bubble staff) but the golden one you can find in the shrine underneath this type can also alter the nearby ocean and maybe call water animal like dolphin etc to ride, as well as do what the normal one does. It would be a good reward for going into the shrine at the end and also build rep with mer shrine.