Main article: Bosses
Duke Fishron is a fish-pig-dragon hybrid with 50,000 health and 50 defense. It is summoned when a Truffle Worm is used as bait with a higher-powered fishing rod in an Ocean biome.
In its first stage, Duke Fishron will attempt to ram the player 5 times before either firing explosive bubbles or summoning Sharknados. In its second stage, Duke Fishron gains glowing eyes and a boost to attack and defense. Although its ramming attacks remain the same, instead of shooting bubbles directly at the player, it flies quickly around in circles, sending bubbles everywhere. Instead of summoning Sharknados in this stage, Duke Fishron summons larger Cthulhunados. These remain in place until Duke Fishron is defeated. Duke Fishron is said to be the hardest boss in the game except for the Moon Lord, but the battle becomes much easier when the player has Wings equipped. Much of the difficulty of the Duke Fishron fight is from his speed, but it can be avoided by going around him in circles while using Wings.
In Expert Mode, when Duke Fishron gets to low enough health, he starts turning invisible and charging at the player with high speed.