Neptune's Crown is a Rare head accessory with a 5% drop chance from the Neptune boss at Fishman Island which is accessible through the Fishman Cave maze.
It gives +1.5 HP Regen.
The level requirement to trade it is 230+.
The accessory is a four-pointed crown with 4 red jewels, 1 on each side, with glowing yellow particles in the middle similar to the Gorilla King Crown.