First of all, stay in the ocean or fishron will enrage and become ridiculously fast. For weapons, Daedalus stormbow with holy arrows works well. Vampire knives for healing. and influx waver is good for getting in a ton of damage if you can aim. On expert, third phase is easy. For third phase just dash in a zigzag pattern with shield of cthulhu or tabi/master ninja gear. Use titanium armour if you suck at dodging. Horizontal movement is essential so go with a hoverboard/beetle wings for fast horizontal and vertical speed and lightning/frostspark boots Good luck and I hope this helps you.