Guide:Duke Fishron strategies

"The mutant terror of the sea..."

Duke Fishron is a tough Hardmode Boss and one of the final Bosses in versions of Terraria. With very high movement speed, high damage and deadly sharknadoes, it is one of the most difficult bosses in the game.

Spawn Condition
Duke Fishron can be spawned by using your with  as Bait.

It must then be defeated within the Ocean or else it will be enraged.

The Fight
Duke Fishron has two phases normally, and a third phase in and.

First Phase
Duke Fishron will attack in three different ways during the first phase. The first thing Fishron will do is begin his charging flurry. He will charge towards the player exactly five times, with a short pause between each charge.

After each charge, he will execute one of the two Projectile attacks:
 * The First attack fires around 20 ;
 * The Second attack will create two small Bubbles on either side of where he is located that will each generate a Sharknado. The Sharknadoes are not only tall and do damage, but they also fire towards the player.

Second Phase
When Duke Fishron falls below 25,000 health, he will stay stationary for a second, then his eyes will glow as he enters his second stage. His damage and speed increase significantly. However, his defense drops to 40.

His charge flurry only has 3 charges, but they are a bit faster than before. He still has two kinds of projectile attacks, but their patterns change:
 * The Detonating Bubble attack now causes him to move around in a circle, dropping the bubbles in a circle around his original location. This spreads out the bubbles, making it more difficult to hit them all.
 * His Sharknado attack upgrades to summon a Cthulhunado. He will fire a special bubble that homes at you and is quite fast(usually unavoidable), but dealing no damage. When it hits you, it will spawn a Cthulhunado, a very tall tornado that does lots of damage and fires large quantities of Sharkrons. It also lasts much longer.

Note that, after the battle is over, care should still be taken. If he has launched a Cthulhunado, it may still fire Sharkrons. He may also have died in the Cthulhunado, so don't charge into it to collect his drops until it dissipates.

Duke Fishron's charging attack is his primary attack, and one of the most difficult to dodge when without proper mobility accessories.

The key to dodging it is to try to move perpendicularly to where he is aimed, right before he makes his charge. For example, if you are horizontal with him when he is about to charge, you need to quickly up (or down, if you're already flying). If he is right above/below you, then you need to quickly move left or right.

One important element of the Sharknado attack is that they will spawn in the location where Duke Fishron was when he fired the attack. And they will despawn almost exactly when he is ready to drop another pair of Sharknadoes.

As long as the player keeps in mind what attack Duke Fishron will do next, the player can put him in a position that makes it hard for the player to hit the Sharknadoes themselves. For example, during the charging flurry before the Sharknado attack, the player can move towards the edge of the screen, horizontally. That way, the player can run the other way knowing that they will not encounter Sharkrons from that direction. This also means that attacks towards Duke Fishron will also be towards the direction of incoming Sharkrons.

Also, note that Duke Fishron's first attack will always be bubbles.

Sharknadoes are quite tall; getting over them will require fast, or

The upgraded Sharknado attack is a bit more difficult to deal with. It's taller, and it does more damage than the original, plus it fires more Sharkrons.

However, there is one thing that makes it a bit easier to deal with: the Cthulhunado will spawn in the location where you were when the bubble hit you. This gives you a bit more control over where the tornado spawns, so you have more of a chance (if you are fast) to make sure it doesn't spawn in an inconvenient place. You likely do not have the speed to outrun the attack, but you can help get it out of the way.

The downside of course is that, once the bubble hits you, you need to quickly move, lest it spawn on top of you. Do not allow the bubble to hit you while you are moving upwards straight or on the ground, or you are likely to take damage from it and possibly stunlocked immediately.

Another important factor to note is that by no means necessary should you attempt to cross a Cthulhunado. They deal about 100 damage, which will turn the fight in Duke Fishron's favor. Always use Wings to fly over them. Alternatively, use the Rod of Discord to teleport to the other side.

Expert Mode
When Duke Fishron drops below 9000 health, he will transform again and the background will notably darken, while making himself invisible except for his glowing eyes.

He will only be able to use his charge attacks in this stage, but he will gain the ability to teleport behind the player before attacking. The charges will come in a set pattern: After teleporting, he will successively charge once, then twice, and finally three times before the pattern resets.

While his contact damage is reduced, the high speed of his charges can cause you to get hit many times in a quick succession. Pay attention to his attack pattern, and make sure to not stand still during the fight. You should also try to get away from any Cthulhunadoes left from the second stage.

Due to the frequency of his teleportation, you may prefer homing or high velocity weapons during this stage.

Terrain Preparation
The arena must be located in the Ocean, unless you're very confident that you can beat an enraged Fishron, which is usually not recommended.


 * Make an arena with 3 - 5 rows of Platforms, each about 50 tiles apart due to the height of the Cthulhunadoes. The arena should span at least the width of the Ocean. can be useful to outrun Duke Fishron's attacks, but since the player cannot travel through them, they can severely limit vertical movement and thus should only be used on the bottom row.
 * The arena must be very tall: the Tornadoes are very tall, and require a significant amount of flight time to fly over.

Gearing up
It's highly recommended to defeat first if you haven't already, as these tips will take that into account. If you have no idea how to reach Golem, check this Walkthrough section.

By this point, you should have 500 Health. If not, it's recommended you use as many as possible. You need to beat at least one of the Mechanical Bosses in order to spawn Life Fruits.

Armor

 * For melee users, the best offensive set consists of the, , and . Alternatively, can be worn if you prefer a hybrid set. If defense is preferred,  can be used with the.
 * For ranged users, the best offensive set consists of the /, , and or.
 * For magic users, the best offensive set consists of either or a hybrid set consisting of, , and .  can be used to heal when your health is running low.
 * For summoners, the best set consists of . For a bit more survivability, can be used.

Weapons
For Melee users:
 * The is a very powerful choice if you have defeated Martian Madness already.
 * The also performs well, though not as well as the Influx Waver.
 * The is an excellent option.
 * Constantly throwing the or  while flying around can defeat him quickly.
 * is the best Yo-yo that can be used at this point.
 * are very useful for stealing life combined with decent damage. Also, the life steal works better on his second phase.
 * is useful to significantly lower Duke Fishron's defense.
 * The is somewhat low in damage, but it makes up for this by homing in on Fishron during the fight.

For Ranged users:
 * The is an extremely powerful choice when used with Crystal Bullets, but will often be unable to target Duke Fishron when he is offscreen.
 * The, , and are also highly effective when using Crystal Bullets. Chlorophyte Bullets are a more accurate but significantly weaker alternative.
 * The and  are nearly as powerful as the guns listed above, and are available earlier in progression.
 * The is very useful with its extremely high  and splitting arrows, dealing damage to the Sharknadoes as well.
 * or will reduce his defense.
 * The is powerful against him, if you have defeated the Frost Moon.
 * The with Ichor or Holy Arrows can perform excellently against him.
 * The is very effective.

For Magic users:
 * The is very strong due to its excellent DPS, although it requires you to get closer than with other weapons.
 * The Nightglow is also very strong because of its homing ability and high DPS.
 * The spell is helpful as it reduces his defense.
 * The does a lot of damage and is also a good choice.
 * The is very good for attacking while he is stationary.
 * The can be used if the player has already defeated the Martian Madness.
 * The can deal a lot of damage and only needs to be cast once in a while.
 * The  is also a viable option.
 * The is effective due to its homing nature allowing one to focus on dodging, especially during the third and final phase in Expert/Master Mode.
 * The, , and are the best pre-Plantera magic weapons against this boss.

For Summoners:
 * The is the best choice available. The  is a weaker alternative.
 * All whips at this stage of the game deal less damage per second than weapons from other classes, even when wearing summoning equipment. They also have relatively short range, making them risky to use against Duke Fishron. If you absolutely must use a whip, the best options are the and, which can occasionally be used to apply tag damage, but should not be used as main weapons.

Accessories

 * are a must-have for the fight. The can make them significantly faster, making it easier to get over the Cthulhunadoes and dodging his attacks while flying.
 * Alternatively, one can obtain the Jetpack. The high vertical speed makes it an ideal choice for dodging Duke Fishron without the need of the Frog Leg, though having the Frog Leg can make it even more effective at dodging Cthulhunadoes. Desktop users can also use the.
 * Desktop users have access to the, which allows for increased ascent speed with wings and fast running, even on normal tiles. On other platforms, or  can still give the increased movement speed.
 * The, , or are incredibly useful for dodging its attacks with their dashing capabilities.
 * Accessories that increase damage are a must have for ending the battle sooner. The best choices include the or, , , and.
 * or is recommended as the boss speed might cause several heavy hits on characters should the boss catch the player. The Sharknados may also flank the player hitting them consecutively especially on Duke Fishron's second phase.
 * Characters with Spectre Armor should consider using or, as the damage dealt by Duke Fishron's attacks will often times completely restore their MP, allowing them to attack constantly while restoring HP. Care should be taken as the boss' high attack can make quick work of reckless players.
 * If you are using or another yoyo, use a.
 * will both allow for increased regen and reduced time for the debuff.
 * The mount is a good replacement for Wings and can be better as it provides infinite air time. Unlike Wings, however, it's much slower and can't be used with a dash.
 * An retains the  ability to protect from the  debuff, and will also provide knockback resistance.
 * The mount can be used in this fight due to its high mobility through water without having to use asphalt blocks.
 * and could help you to move fast vertically, which could be extremely useful during the 3rd phase of Duke Fishron.

Potions and Buffs
As with any other Hardmode boss, it would be useful to prepare the following potions:
 * is highly recommended as it will destroy the Detonating Bubbles Fishron spawns before they reach the player.
 * and to survive. Two of each will last enough.
 * and potions for even greater survivability.
 * Any food item that can provide the buff is very welcome.
 * helps you a lot to evade the Duke and its attacks.
 * and/or for a boost in damage output.
 * and potions are a must for Magic users.
 * If a player has no arena, they can just use.
 * can free up an accessory slot, but it's recommended to use with them.
 * Melee characters should use the debuff and the  if available.
 * If you are facing him at night, a, , and will help a lot so that you don't have to worry about visibility.

Minecart Strategy
This strategy differs from others in that it doesn't use a skybridge, replacing it with looped minecart track above the ocean, so the player won't have to deal with his enraged behavior. It does, however, need some more work than other ones, especially when building the arena.

Materials

 * 600-1200 normal minecart tracks for building loop + 2 booster tracks
 * Any kind of hammer

Arena Preparation
The essence is to make looped minecart track approx. 60 tiles above Ocean itself. It should consist of at least 600 tiles; while shape is pretty loose, it should have at least two places in which player drastically changes altitude, as well as at least 100 tiles long flats.

One should also make a "Starter" - a short molo with boosters, from which player will summon Duke Fishron and quickly escape to the loop.

It should be noted also that arena shouldn't exceed Ocean biome.

Execution
When everything's done, player should sit in a minecart on "Starter" and summon the Fishron. As soon as it's done, one should quickly go to loop (boosters will help). At this point, everything that remains is to shoot Fishron while maintaining speed on track, healing a/o replenishing mana when needed. Some tips:
 * Use a homing weapon, especially if your arena is pretty large. Fishron will spend most time off-screen, and high speed will often change directions you're facing.
 * Though stock minecart shouldn't be used, Mechanical Cart is not a good choice. Even though with it provides defense bonus, as well as speed to avoid Fishron's charges, it can easily outrun him causing Fishron to despawn, which is possible on larger arenas. Higher speed means also that you will more often run into Sharknados.
 * Try to make arena consisting of approx. 800 tiles, but don't make it horizontally-long. If you do so, Fishron will frequently run into you, and Cthulunados in his second stage will quickly kill you as there won't be any way to dodge them.

Abuse of Invincibility Frames
Standing in Lava with an Obsidian Rose and a Cross Necklace equipped will give the player invincibility frames for almost all of the fight while taking extremely little damage from the Lava due to the Rose's effects. this can also be done standing on a Spike.

Enraged Anti-Gravity Hook Strategy
When Enraged, Duke Fishron is much faster and does much more damage. But with this stategy, this strength can be turned into a weakness. What you must do is get an Anti-Gravity Hook and place one or more platforms in the air. After Duke Fishron becomes enraged, you use your Anti-Gravity Hook in the platform and start using it to spin in a circle. This makes it possible to dodge all attacks. Keep in mind that this strategy only works with enraged Duke Fishron, because in his enraged behavior he will do nothing but attempt to ram you. Then you use the hook on the platform, start spinning and dodge his charges.

Giant Ocean strategy
Creating a massive ocean as wide as the world size allows, tall enough that you're only about 20 tiles under the height where harpies start spawning, and filling it with water will create a massive areana to fight in using the cute fishron, or lava shark mounts, allowing unprecedented mobility, freeing up accessory slots we can fill with damage. Drinking the standard damage buff potions, swiftness, and class specific buffs like ammo reservation or magic power. The hunter potion is quite invaluable using this strategy because the hunter potion allows the player to see the boss at all times. Setting up some underwater lighting like coral torches or living fire blocks is also recommended otherwise the sharknados are going to be nigh-impossible to see. For experienced players, this is a surprisingly safe and effective way to fight the Duke, even in master mode.

Use the gills potion or neptune's shell so you dont drown. Stopping for air is not the best idea against a boss as quick and agile as the duke

You Want My Health? I'll Take Yours Strategy
Using the UFO mount(with a platform on the ocean to catch the supplies), and use a recommended weapon that is not the Vampire Knives. However, once he deals damage, start using the Vampire Knives. Because what time it is doesn't matter, you can repeat this strategy until he falls. "The mutant terror of the sea..."

Duke Fishron is a tough Hardmode Boss and one of the final Bosses in versions of Terraria. With very high movement speed, high damage and deadly sharknadoes, it is one of the most difficult bosses in the game.

Spawn Condition
Duke Fishron can be spawned by using your with  as Bait.

It must then be defeated within the Ocean or else it will be enraged.

The Fight
Duke Fishron has two phases normally, and a third phase in and.

First Phase
Duke Fishron will attack in three different ways during the first phase. The first thing Fishron will do is begin his charging flurry. He will charge towards the player exactly five times, with a short pause between each charge.

After each charge, he will execute one of the two Projectile attacks:
 * The First attack fires around 20 ;
 * The Second attack will create two small Bubbles on either side of where he is located that will each generate a Sharknado. The Sharknadoes are not only tall and do damage, but they also fire towards the player.

Second Phase
When Duke Fishron falls below 25,000 health, he will stay stationary for a second, then his eyes will glow as he enters his second stage. His damage and speed increase significantly. However, his defense drops to 40.

His charge flurry only has 3 charges, but they are a bit faster than before. He still has two kinds of projectile attacks, but their patterns change:
 * The Detonating Bubble attack now causes him to move around in a circle, dropping the bubbles in a circle around his original location. This spreads out the bubbles, making it more difficult to hit them all.
 * His Sharknado attack upgrades to summon a Cthulhunado. He will fire a special bubble that homes at you and is quite fast(usually unavoidable), but dealing no damage. When it hits you, it will spawn a Cthulhunado, a very tall tornado that does lots of damage and fires large quantities of Sharkrons. It also lasts much longer.

Note that, after the battle is over, care should still be taken. If he has launched a Cthulhunado, it may still fire Sharkrons. He may also have died in the Cthulhunado, so don't charge into it to collect his drops until it dissipates.

Duke Fishron's charging attack is his primary attack, and one of the most difficult to dodge when without proper mobility accessories.

The key to dodging it is to try to move perpendicularly to where he is aimed, right before he makes his charge. For example, if you are horizontal with him when he is about to charge, you need to quickly up (or down, if you're already flying). If he is right above/below you, then you need to quickly move left or right.

One important element of the Sharknado attack is that they will spawn in the location where Duke Fishron was when he fired the attack. And they will despawn almost exactly when he is ready to drop another pair of Sharknadoes.

As long as the player keeps in mind what attack Duke Fishron will do next, the player can put him in a position that makes it hard for the player to hit the Sharknadoes themselves. For example, during the charging flurry before the Sharknado attack, the player can move towards the edge of the screen, horizontally. That way, the player can run the other way knowing that they will not encounter Sharkrons from that direction. This also means that attacks towards Duke Fishron will also be towards the direction of incoming Sharkrons.

Also, note that Duke Fishron's first attack will always be bubbles.

Sharknadoes are quite tall; getting over them will require fast, or

The upgraded Sharknado attack is a bit more difficult to deal with. It's taller, and it does more damage than the original, plus it fires more Sharkrons.

However, there is one thing that makes it a bit easier to deal with: the Cthulhunado will spawn in the location where you were when the bubble hit you. This gives you a bit more control over where the tornado spawns, so you have more of a chance (if you are fast) to make sure it doesn't spawn in an inconvenient place. You likely do not have the speed to outrun the attack, but you can help get it out of the way.

The downside of course is that, once the bubble hits you, you need to quickly move, lest it spawn on top of you. Do not allow the bubble to hit you while you are moving upwards straight or on the ground, or you are likely to take damage from it and possibly stunlocked immediately.

Another important factor to note is that by no means necessary should you attempt to cross a Cthulhunado. They deal about 100 damage, which will turn the fight in Duke Fishron's favor. Always use Wings to fly over them. Alternatively, use the Rod of Discord to teleport to the other side.

Expert Mode
When Duke Fishron drops below 9000 health, he will transform again and the background will notably darken, while making himself invisible except for his glowing eyes.

He will only be able to use his charge attacks in this stage, but he will gain the ability to teleport behind the player before attacking. The charges will come in a set pattern: After teleporting, he will successively charge once, then twice, and finally three times before the pattern resets.

While his contact damage is reduced, the high speed of his charges can cause you to get hit many times in a quick succession. Pay attention to his attack pattern, and make sure to not stand still during the fight. You should also try to get away from any Cthulhunadoes left from the second stage.

Due to the frequency of his teleportation, you may prefer homing or high velocity weapons during this stage.

Terrain Preparation
The arena must be located in the Ocean, unless you're very confident that you can beat an enraged Fishron, which is usually not recommended.


 * Make an arena with 3 - 5 rows of Platforms, each about 50 tiles apart due to the height of the Cthulhunadoes. The arena should span at least the width of the Ocean. can be useful to outrun Duke Fishron's attacks, but since the player cannot travel through them, they can severely limit vertical movement and thus should only be used on the bottom row.
 * The arena must be very tall: the Tornadoes are very tall, and require a significant amount of flight time to fly over.

Gearing up
It's highly recommended to defeat first if you haven't already, as these tips will take that into account. If you have no idea how to reach Golem, check this Walkthrough section.

By this point, you should have 500 Health. If not, it's recommended you use as many as possible. You need to beat at least one of the Mechanical Bosses in order to spawn Life Fruits.

Armor

 * For melee users, the best offensive set consists of the, , and . Alternatively, can be worn if you prefer a hybrid set. If defense is preferred,  can be used with the.
 * For ranged users, the best offensive set consists of the /, , and or.
 * For magic users, the best offensive set consists of either or a hybrid set consisting of, , and .  can be used to heal when your health is running low.
 * For summoners, the best set consists of . For a bit more survivability, can be used.

Weapons
For Melee users:
 * The is a very powerful choice if you have defeated Martian Madness already.
 * The also performs well, though not as well as the Influx Waver.
 * The is an excellent option.
 * Constantly throwing the or  while flying around can defeat him quickly.
 * is the best Yo-yo that can be used at this point.
 * are very useful for stealing life combined with decent damage. Also, the life steal works better on his second phase.
 * is useful to significantly lower Duke Fishron's defense.
 * The is somewhat low in damage, but it makes up for this by homing in on Fishron during the fight.

For Ranged users:
 * The is an extremely powerful choice when used with Crystal Bullets, but will often be unable to target Duke Fishron when he is offscreen.
 * The, , and are also highly effective when using Crystal Bullets. Chlorophyte Bullets are a more accurate but significantly weaker alternative.
 * The and  are nearly as powerful as the guns listed above, and are available earlier in progression.
 * The is very useful with its extremely high  and splitting arrows, dealing damage to the Sharknadoes as well.
 * or will reduce his defense.
 * The is powerful against him, if you have defeated the Frost Moon.
 * The with Ichor or Holy Arrows can perform excellently against him.
 * The is very effective.

For Magic users:
 * The is very strong due to its excellent DPS, although it requires you to get closer than with other weapons.
 * The Nightglow is also very strong because of its homing ability and high DPS.
 * The spell is helpful as it reduces his defense.
 * The does a lot of damage and is also a good choice.
 * The is very good for attacking while he is stationary.
 * The can be used if the player has already defeated the Martian Madness.
 * The can deal a lot of damage and only needs to be cast once in a while.
 * The  is also a viable option.
 * The is effective due to its homing nature allowing one to focus on dodging, especially during the third and final phase in Expert/Master Mode.
 * The, , and are the best pre-Plantera magic weapons against this boss.

For Summoners:
 * The is the best choice available. The  is a weaker alternative.
 * All whips at this stage of the game deal less damage per second than weapons from other classes, even when wearing summoning equipment. They also have relatively short range, making them risky to use against Duke Fishron. If you absolutely must use a whip, the best options are the and, which can occasionally be used to apply tag damage, but should not be used as main weapons.

Accessories

 * are a must-have for the fight. The can make them significantly faster, making it easier to get over the Cthulhunadoes and dodging his attacks while flying.
 * Alternatively, one can obtain the Jetpack. The high vertical speed makes it an ideal choice for dodging Duke Fishron without the need of the Frog Leg, though having the Frog Leg can make it even more effective at dodging Cthulhunadoes. Desktop users can also use the.
 * Desktop users have access to the, which allows for increased ascent speed with wings and fast running, even on normal tiles. On other platforms, or  can still give the increased movement speed.
 * The, , or are incredibly useful for dodging its attacks with their dashing capabilities.
 * Accessories that increase damage are a must have for ending the battle sooner. The best choices include the or, , , and.
 * or is recommended as the boss speed might cause several heavy hits on characters should the boss catch the player. The Sharknados may also flank the player hitting them consecutively especially on Duke Fishron's second phase.
 * Characters with Spectre Armor should consider using or, as the damage dealt by Duke Fishron's attacks will often times completely restore their MP, allowing them to attack constantly while restoring HP. Care should be taken as the boss' high attack can make quick work of reckless players.
 * If you are using or another yoyo, use a.
 * will both allow for increased regen and reduced time for the debuff.
 * The mount is a good replacement for Wings and can be better as it provides infinite air time. Unlike Wings, however, it's much slower and can't be used with a dash.
 * An retains the  ability to protect from the  debuff, and will also provide knockback resistance.
 * The mount can be used in this fight due to its high mobility through water without having to use asphalt blocks.
 * and could help you to move fast vertically, which could be extremely useful during the 3rd phase of Duke Fishron.

Potions and Buffs
As with any other Hardmode boss, it would be useful to prepare the following potions:
 * is highly recommended as it will destroy the Detonating Bubbles Fishron spawns before they reach the player.
 * and to survive. Two of each will last enough.
 * and potions for even greater survivability.
 * Any food item that can provide the buff is very welcome.
 * helps you a lot to evade the Duke and its attacks.
 * and/or for a boost in damage output.
 * and potions are a must for Magic users.
 * If a player has no arena, they can just use.
 * can free up an accessory slot, but it's recommended to use with them.
 * Melee characters should use the debuff and the  if available.
 * If you are facing him at night, a, , and will help a lot so that you don't have to worry about visibility.

Minecart Strategy
This strategy differs from others in that it doesn't use a skybridge, replacing it with looped minecart track above the ocean, so the player won't have to deal with his enraged behavior. It does, however, need some more work than other ones, especially when building the arena.

Materials

 * 600-1200 normal minecart tracks for building loop + 2 booster tracks
 * Any kind of hammer

Arena Preparation
The essence is to make looped minecart track approx. 60 tiles above Ocean itself. It should consist of at least 600 tiles; while shape is pretty loose, it should have at least two places in which player drastically changes altitude, as well as at least 100 tiles long flats.

One should also make a "Starter" - a short molo with boosters, from which player will summon Duke Fishron and quickly escape to the loop.

It should be noted also that arena shouldn't exceed Ocean biome.

Execution
When everything's done, player should sit in a minecart on "Starter" and summon the Fishron. As soon as it's done, one should quickly go to loop (boosters will help). At this point, everything that remains is to shoot Fishron while maintaining speed on track, healing a/o replenishing mana when needed. Some tips:
 * Use a homing weapon, especially if your arena is pretty large. Fishron will spend most time off-screen, and high speed will often change directions you're facing.
 * Though stock minecart shouldn't be used, Mechanical Cart is not a good choice. Even though with it provides defense bonus, as well as speed to avoid Fishron's charges, it can easily outrun him causing Fishron to despawn, which is possible on larger arenas. Higher speed means also that you will more often run into Sharknados.
 * Try to make arena consisting of approx. 800 tiles, but don't make it horizontally-long. If you do so, Fishron will frequently run into you, and Cthulunados in his second stage will quickly kill you as there won't be any way to dodge them.

Abuse of Invincibility Frames
Standing in Lava with an Obsidian Rose and a Cross Necklace equipped will give the player invincibility frames for almost all of the fight while taking extremely little damage from the Lava due to the Rose's effects. this can also be done standing on a Spike.

Enraged Anti-Gravity Hook Strategy
When Enraged, Duke Fishron is much faster and does much more damage. But with this stategy, this strength can be turned into a weakness. What you must do is get an Anti-Gravity Hook and place one or more platforms in the air. After Duke Fishron becomes enraged, you use your Anti-Gravity Hook in the platform and start using it to spin in a circle. This makes it possible to dodge all attacks. Keep in mind that this strategy only works with enraged Duke Fishron, because in his enraged behavior he will do nothing but attempt to ram you. Then you use the hook on the platform, start spinning and dodge his charges.

Giant Ocean strategy
Creating a massive ocean as wide as the world size allows, tall enough that you're only about 20 tiles under the height where harpies start spawning, and filling it with water will create a massive areana to fight in using the cute fishron, or lava shark mounts, allowing unprecedented mobility, freeing up accessory slots we can fill with damage. Drinking the standard damage buff potions, swiftness, and class specific buffs like ammo reservation or magic power. The hunter potion is quite invaluable using this strategy because the hunter potion allows the player to see the boss at all times. Setting up some underwater lighting like coral torches or living fire blocks is also recommended otherwise the sharknados are going to be nigh-impossible to see. For experienced players, this is a surprisingly safe and effective way to fight the Duke, even in master mode.

Use the gills potion or neptune's shell so you dont drown. Stopping for air is not the best idea against a boss as quick and agile as the duke

You Want My Health? I'll Take Yours Strategy
Using the UFO mount(with a platform on the ocean to catch the supplies), and use a recommended weapon that is not the Vampire Knives. However, once he deals damage, start using the Vampire Knives. Because what time it is doesn't matter, you can repeat this strategy until he falls.