how i can beat him please i need help?

Tide Remember you can’t freeze this npc. Welldweller Cuirass, Eternal, Daemon, Pirate Cutlass, Graverobbers Shovel, Sponge, Hydrus Armor or Phaloroceas Rain Charm (defends water) and Unlimited use % healer for bigger pet or Red Rreign Staff of Lore for smaller pets

If you don't have a big budget, here's a method for 25 k.

equip two Azathoth Waist Tunic to your pet. They each reflect 1-100 percent water, so having two will increase your luck. I used it before and I got away with plentiful health left.

But they upgraded the Aquatic Wand of Blasting Torpedication, making wind and fire dangerous as well, so you might have to steal/blast that one first.

Thank you guys