You'll have quite a cozy time when you first explore the waters in Dave The Diver, but it'll constantly get more dangerous as you progress in the story. There will be times when you'll face a boss enemy. You'll have to defeat most of these enemies to progress the story, but some of them are optional.
Mantis Shrimp is one of the optional bosses in the game, and you can find it quite easily once you meet the required conditions. Although, defeating it won't be as easy since you have to follow a specific pattern.
How To Find Mantis Shrimp Boss
If you're just starting out in Dave The Diver, it'll take you quite a long time to get to this boss. After progressing the main story a little, you'll get to meet an NPC named Sato. He'll unlock the Marinca app for you where you can get cards for every fish you catch, and the rarity of the card is the same as the fish you catch.
Once you unlock this and get a stormy night, Sato will come to your boat and tell you that a rare boss has been sighted in the waters. You'll have to dive on the same night to find the boss. Although, the first time this happens, you'll face a boss called Truck Hermit Crab. The second time will be where Mantis Shrimp appears.
If you dive at nighttime, one-third of the time will be taken away from the restaurant, so you'll earn less on that day.
As you dive on a stormy night, you'll have to look for a white vortex that can spawn anywhere between the depth of zero to 50. You can enter the vortex to face the Shrimp, but keep in mind that you'll need heavy artillery if you want to defeat it without having to restart the battle multiple times.
Moreover, these bosses only start appearing after you get the new gloves from Udo since you need to pick up heavy items in these fights.
How To Defeat Mantis Shrimp
Mantis Shrimp always blocks its eyes with the gloves and your bullets won't do any damage to the other parts of its body, so you can't brute force this fight. When the boss uses its left hand to throw a charged punch, it'll reveal its eyes for a few seconds, which is the perfect opportunity to deal damage.
When the fight starts, position yourself on the left side of the battlefield just below the boss. When you do this, the punches thrown by the boss won't hit you. Stay in this position until it uses the left-hand punch and then use the sprint swimming to quickly get back to the top and hit its eye.
You'll mostly be able to hit the boss only once before it hides its eyes again, so it's recommended to use a high-damage weapon like Sniper Rifle.
Once you hit it in the eye, it'll perform an attack where it jumps back and produces a water current going to the left soon after. When this attack happens, you'll see a lever appearing on the top-left side of the battlefield. This is why it's important to stay as far left as you can while avoiding the spikes on the left wall.
Once the lever spawning animation finishes, you'll be able to swim to it and pull it down. The camera will zoom into the boss for a second after the animation finishes, but you can swim to the lever even during this closeup. Pull the lever down until the yellow object at the bottom comes to the middle of the field.
You have to do this quickly as the Mantis boss will be charging a punch all this time.
If you take too much time, the lever will go away and you'll be pushed back into the spikes to take damage.
When you successfully bring the object in the correct position, the Shrimp will punch it and go into a vulnerable state for a few seconds. This is the perfect time to quickly swim to it and hit its eyes as much as you can. Another reason why a Sniper Rifle is good here is that you'll have to swim lesser, allowing you to get more hits.
When the Shrimp recovers from the vulnerable state, you can go back below its arms and follow this cycle until it's defeated. It's recommended to not go above the Shrimp's body no matter what as it will perform an attack that slams you to the ceiling, which will deal a heavy blow to your oxygen.
You have to use fast swimming a lot in this battle, so you have to avoid all damage since your oxygen already depletes faster.
There is only one oxygen tube on the battlefield, but you can bring portable tanks from yellow chests if you get lucky enough to find them.
Once the boss is defeated, you can harvest its meat and go back to the surface. This meat will open a new recipe in the "Research" tab called Boiled Mantis Shrimp With Soy Paste, and this recipe only takes one Artisan's Flame to learn. You can serve the dish to multiple people with just one of these dishes, but you also won't get it again.
Finally, you'll also unlock a shiny Marinca card for the boss.