If you've reached the sixth chapter of Dave The Diver, you've already unlocked most of the areas in the game. This chapter requires you to go around Glacial Area and activate three switches to open the Control Room, but you'll have to battle about three bosses in this chapter apart from solving numerous puzzles.
Helicoprion is one of these three bosses, and you'll be fighting it alongside one of the Sea People who you met at the start. You might not last long in this fight unless you know the exact mechanic that you need to use against the giant fish.
How To Find Helicoprion
Since it's one of the main story bosses, you're guaranteed to find it once you reach the correct place. As you're going through different domains in the Glacial Area, you'll eventually lower the heat and be able to access the bottom region. Here, you'll enter the third domain alongside Suwam.
In this domain, Dave and Suwam get together and restore the water level so that both of them can go freely around the area. When you're just about to reach the third switch, you'll enter the boss battle room where Helicoprion will instantly aggro onto you. Suwam will teleport to a platform at the top and hide there.
In this entire domain, you use both Dave and Suwam at the same time, and this process remains the same during this boss fight.
Helicoprion Attack Pattern
Once the battle starts, Helicoprion will constantly throw a barrage of attacks at Dave, and you won't lose its aggro no matter where you go. It essentially has two types of attacks: Slash attack and Dash attack. The Slash attack is similar to the Hammerhead shark's attack where it swings its face nearby twice and then dashes in the direction it's facing to launch the final attack.
To dodge this, you simply have to stay close to the fish and go up or down as soon as it starts charging the attack. If you get hit by any of these slashes, you'll take quite a lot of damage. Moreover, if you're not near the fish, it'll perform a dash attack where it constantly runs in a specific direction while the wheel on its head destroys everything in its path.
Helicoprion can also change directions sometimes while doing the dash attack, so be careful of that.
Since it's quite hard to dodge the fish's attacks, there are plenty of random rock structures on the battlefield. You can find them on the bottom level, on both the left and right platforms at the higher level, and below the platform that Suwam is on. If you run Helicoprion into these rocks, it'll get stuck there until the structure is broken.
Keep in mind that all these structures are one-time use, so you can't keep using them forever. You can also find an ammo refill on the lower platform and the upper right platform, a weapon chest on the upper right platform, and an oxygen refill on the upper left platform.
How To Defeat Helicoprion
To defeat the boss, you'll have to make use of the Divine Fruits near the platform that Suwam is on. First, head over to the weapon chest on the upper right platform and unlock it. This will either give you an upgrade for the current weapon or one of the better weapons for dealing with this boss.
Once you have the weapon, get close to one of the Divine Fruits on Suwam's platform. Make sure Suwam is also close to the fruit you're planning to use. Wait for Helicoprion to come close to the fruit and strike it to disable the fish for a few seconds. This will give you a long window to constantly fire at the enemy.
You can usually finish your weapon's entire magazine while the fish is disabled if you shoot fast enough.
As soon as Helicoprion comes out of the vulnerable state, it'll do the Slash attack almost instantly. Don't get carried away while shooting it or you're bound to take damage from this attack. Once you use a Divine Fruit, it'll get disabled for a few seconds and you'll have to either use the other one on the other side of the platform or kite the enemy for a bit.
After doing enough damage to the fish, it'll wiggle around and hit the wall to the right, opening the passage to the switch room. You can harvest the enemy's body to get its meat and unlock the Roasted Helicoprion Tale recipe in the Research tab at Bancho Sushi. It only takes one Artisan's Flame to get this, but you can only serve it one day.
Portable oxygen tanks and Underwater Scooters are the best items you can bring to this fight.
The tanks will help you in case you take a lot of damage while the Scooters can be used to easily dodge the Slash attack.
Once you defeat Helicoprion, you'll have to fight another boss near the Control Room soon after.