If you've activated the three switches in Glacial Area and reached the Control Room in Dave The Diver, you've already fought a handful of bosses with unique mechanics. Before getting into the final chapter, you'll have to fight another boss right above the Control Room's entrance.
This boss fight will start as a fight against John Watson for the third time, but it'll soon be taken over by Kronosaurus. This giant alligator-like creature will give you quite a hard time with its rapid attacks and high health, though you'll also get a special weapon to defeat it.
Kronosaurus Attack Pattern
After defeating Helicoprion and activating the third switch alongside Suwam, you'll be asked to get to the Control Room's entrance. You'll see a familiar foe as soon as you reach the area. John Watson will come out of his submarine with a brand-new set of attacks to defeat you once and for all, and he won't back down even after you expose him.
During this portion of the fight, you simply have to dodge his missiles since you won't have a Baseball Bat to deflect them this time. After dodging a few attacks, a giant enemy will break out of the walls on the right side and eat John Watson up within seconds. This will be your real enemy in this area.
It's highly recommended to not use any bullets on John Watson since he doesn't take damage from them.
You'll need all the bullets possible for the Kronosaurus fight.
Kronosaurus has three main attacks, and one of them is a common dash that you've seen almost every other boss perform. In this attack, the enemy charges directly at you with its mouth open. You take damage if you hit any part of its body, but the damage is much higher if you get bitten by its jaws.
The boss' body is quite huge, which makes it hard to dodge these attacks. After every few seconds, the boss will suck up a bunch of boulders from the surrounding. It will then charge these boulders for a few seconds and launch them in an arc-shaped pattern. You can easily dodge this attack by swimming in between these boulders or heading straight up.
The third attack is the deadliest and the hardest to dodge. After taking enough damage, Kronosaurus will quickly swim to one side of the battlefield and launch a fire laser attack. This laser will start from just below the boss' body and go up slowly. The only way to dodge this attack is to know exactly when the boss is going to perform it.
If you see Kronosaurus desperately swimming to one end of the battlefield instead of directly coming at you, try to swim on the same side and get under the boss as fast as possible. If that's not possible, you can also swim straight up and reach a higher level than the boss to avoid the attack.
This is one of the hardest-hitting enemy attacks in the game, and it can easily take away half your oxygen even if your suit is fully upgraded.
How To Beat Kronosaurus
Now that you know the boss' attack pattern, you'll also have to learn a special mechanic if you want to defeat Kronosaurus quickly. As soon as the battle starts, head to the left side first and open the weapon chest there. This will either give you a weapon that's much more suited for this battle or an upgrade for your current weapon.
Once you have the new weapon, you can try to shoot at the boss whenever you get a chance. You'll also see a special weapon that was dropped on the battlefield when John Watson got eaten. You can pick this weapon up and use it on the boss once every few seconds as well. Keep in mind that this weapon has a long lock-on phase.
When you're close to Kronosaurus and looking in its direction, you'll be able to start the locking process with the weapon. Once the icon on the boss turns green, you can shoot a rocket that will not only deal a ton of damage but also stagger the boss for a second. The weapon starts sparking for a few seconds after that.
You should try to use the weapon when the boss is charging an attack since it can stagger Kronosaurus and cancel this attack.
The missile launcher automatically recovers in a few seconds, but it also recovers when the boss tries to suck it in with the surrounding boulders. Whenever the weapon is ready to use, it'll start blinking with white light. On the other hand, you won't even be able to pick it up while it's sparking.
There's not a single normal weapon that will completely defeat this boss unless you've already spent a lot of time fully upgrading them, so you'll need the missile launcher's help. You also get a yellow chest on the left side that can give you a portable oxygen tank or an underwater scooter. Both of these items can save your life during this fight.
If you get defeated by Kronosaurus, you can either restart the battle or give up and head back to the boat with everything in your inventory.
Although, if you give up, it'll automatically be nighttime when you reach the boat even if you fought the boss in the morning.