Duke Fishron

Duke Fishron is a Hardmode boss. While he can be summoned as soon as Hardmode is initiated, he can pose a serious threat to new or underprepared players and should be fought later on in the game. Some players may challenge him with post-mechanical bosses gear, but most players may want to wait until post-Golem to battle him. Fighting Duke Fishron is completely optional and not required for, but his defeat will reward the player with powerful weapons.

On the, Duke Fishron and Ocram are the final bosses due to the lack of the Moon Lord in these versions.

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Summoning
Duke Fishron is summoned by fishing in the Ocean using a Truffle Worm as bait. The Truffle Worm is a rare critter that must be caught with the Bug Net, Golden Bug Net, or Lavaproof Bug Net in an underground Glowing Mushroom biome. Once the bobber bobs, reeling in the line spawns Duke Fishron, who emerges from the water, pauses for a moment, and then begins attacking the player.

Summoning Duke Fishron does not require that any other bosses have been defeated beforehand, so on a technical level, he is only restricted by the Hardmode exclusive Truffle Worm, which can be used to spawn him in any world. If within the Ocean biome, he can also be summoned by fishing in lava or honey. The player's Fishing Power is irrelevant to the summoning, and Crate or Sonar potions will be wasted.

Debuffs
When hitting the player in Expert Mode or Master Mode, Duke Fishron has a 33% chance to inflict Bleeding and a 33% chance to inflict Feral Bite. Bleeding can be ignored with an Adhesive Bandage or any of its upgrades, and all of Feral Bite's side effects will be prevented by the Ankh Charm or Ankh Shield.

First stage
Duke Fishron lunges at the player exactly five times, traveling through blocks, before using one of two projectile attacks in this order:


 * : Duke Fishron blows roughly 10-20 bubbles from his mouth that follow the player at moderate speed, exploding and dealing damage on contact. The bubbles can be destroyed by any attack or projectile. These inflict the Wet debuff for 3-8 seconds. Duke Fishron will either move to the top left or top right of the player's location before starting the attack. This attack is affected by wind. The Sharkron attack has the opposite direction of this attack, but it changes each time Duke Fishron is summoned.
 * : Duke Fishron waves his fins, summoning liquid blobs that fall (bypassing any platforms) until they travel 1.5x the vertical size of the screen or impact with blocks. They then spawn Sharknadoes: giant water tornadoes which are 29 blocks high and each fire several Sharkrons. Sharkrons have limited flight range, are destroyed on impact with blocks, and can be killed by the player.

Second stage
When Duke Fishron falls below 50% ( / / ) health, he remains stationary for a second and transforms, being a good time to deal damage and/or consume Potions. His skin becomes a darker green and his eyes will start glowing. His damage and speed increase significantly, but his defense is reduced to 40. His lunges become faster, and are only performed three times instead of five before executing one of his projectile attacks, which are also upgraded:


 * Detonating Bubbles are now fired while Duke Fishron flies in quick loops, which leave a trail of the bubbles behind. This attack will start in the same location relative to the player as the first stage detonating bubble.
 * There is now only one "blob" that causes a tornado, but it follows the player, creating a Cthulhunado on the ground directly below the player (if the player is 95 blocks/190 feet above the surface directly below them, the blob will instead detonate on top of them). Cthulhunadoes are significantly bigger than Sharknadoes (58 blocks high, 23 blocks wide, 11 blocks from the center) and will spawn twice as many Sharkrons; they also deal double the damage of Sharknadoes.

Third stage
When Duke Fishron falls below 15% ( / ) health, he will stop moving to transform again, and the background will be covered in a dark, blue fog. Duke Fishron will become invisible, but his eyes still glow. His damage will be reduced to /, his defense will drop all the way to , and he will only attack by charging at the player, but he gains the ability to teleport behind them before doing so. His charges will come in a set pattern:
 * First, he will charge once before teleporting;
 * Then, he will charge twice, and teleport behind the player again;
 * Finally, he will charge three times, and the pattern will reset.

After being defeated, the background will return to normal, and his Treasure Bag will be dropped.

Tips

 * Keep in mind your current distance from the Ocean that the boss was spawned at, to prevent him from becoming enraged and making the fight unnecessarily more difficult.
 * The Inferno Potion can come in very handy during this fight to prevent taking any damage from Duke's homing bubble attacks. Since they are destroyed when damaged, the Inferno Potion's ring of fire will block them off completely.
 * Players can build a platform along the top of the Ocean to avoid sinking. Water Walking Boots or Water Walking Potions can be used as a substitute for platforms.
 * Duke Fishron's charges aim for where the player is, not where they will be. Because of this, moving perpendicularly with his charges will cause him to completely miss. Dodging his charges can be as simple as moving in a zig-zag pattern or a triangle, or utilizing equipment such as the Crystal assassin set, Shield of Cthulhu, Solar flare set or Tabi.
 * He is the only boss that is immune to the Stunned debuff, making Heart Arrows useless against him.
 * As Cthulhunadoes might be hard to see during nighttime, it is recommended to fight Duke Fishron during the day or use visual aids like the Shine Potion and Hunter Potion.
 * Using an on a block and continuously going in circles can successfully allow dodging every attack and dash from the boss when it is enraged.
 * In, the Shield of Cthulhu can be used to great effect, providing brief invincibility frames when dashing into him.
 * Though its difficulty makes it a post-Plantera or Golem boss, it is possible to defeat Duke Fishron before any Mechanical boss and obtain his drops to greatly ease the fight against them. Using some basic weapons like the Crystal Serpent, Daedalus Stormbow with Holy Arrows, and the Golden Shower can make defeating him a bit easier and will make a good majority of Hardmode a lot easier to progress through.

Trivia

 * Duke Fishron is the only boss with more Debuff immunities in his second stage than in his first
 * Duke Fishron was originally part of an April Fools joke by Re-Logic that claimed an "Aquarian Horde" event was to be included in the game. Ultimately, only Duke Fishron made it into the game.
 * In the Wii U edition, the second phase's eyes will only glow when transforming and summoning Cthulhunadoes.
 * Duke Fishron resembles a mutant creature in the second episode in the fourth season of the American animated science fiction sitcom Futurama, Leela's Homeworld.
 * The Sharknado attack is an allusion to the 2013 American made-for-television sci-fi disaster film Sharknado.
 * Duke Fishron turns transparent when over blocks, much the same way that Pigrons do.
 * The Treasure Bag's image more resembles an actual pig, as it lacks the Fangs that Duke Fishron has.
 * Duke Fishron drops an absurdly low amount of coins compared to other Hardmode bosses, despite being one of the toughest to defeat.
 * Duke Fishron's weapon drops have considerably low reforge costs compared to other weaponry acquired around the same time.
 * Duke Fishron (and by extension, the Cute Fishron) appears to be a combination of a shark, a pig, and a dragon. Cenx confirmed that the Pigron was a cross between the latter two creatures, which further proves this theory.
 * The Cthulhunado could be a reference to Cthulhu's avatar the "Father of All Sharks".
 * While fishing with a Truffle Worm and a Sonar Potion, it shows as a normal catch, however reeling the line in still summons Duke Fishron.
 * Duke Fishron is the only boss with three distinct stages, one being Expert-mode exclusive.
 * Duke Fishron is the only Hardmode boss that does not have to be defeated to progress the game.
 * On the, along with Duke Fishron, the Empress of Light and Queen Slime are also Hardmode bosses that do not have to be defeated to progress the game.
 * Duke Fishron is one of 6 bosses with exclusive music, the others being Queen Bee, Queen Slime, Empress of Light, Plantera, and Moon Lord.