It's somewhat unexpected that Moonglow Bay is a little more than a sim where you catch a few fish. You can also cook homemade dishes and bond with the townsfolk, and saving the town both in a morale and economic sense is what drives the main story. The town is scared of the legends found deep in the ocean, and it's halted thriving fishing businesses. But by "defeating" each boss, you can bring the town back to life. Follow the guide for each boss fish below to finish each chapter with ease.
Moonglow Bay Chapter 1 Boss: Confront the Ruin of Ships
Down in the hidden lake, you'll find that the monster everyone was scared of is actually just a barnacle whale who's probably so upset because he has a few harpoons in him. The goal here is probably pretty obvious -- you need to remove the harpoons -- but it can be a bit tricky.
There are three harpoons to pull out of the barnacle whale, and each harpoon is more difficult than the last. Approach the whale with your boat, but be mindful not to get too close -- when the whale swims away, it can severely damage your boat. Cast your fishing line onto one of the harpoons; you'll know you can grab onto it if it's highlighted with a white outline. Then, reel it in.
Keep an eye on the fishing line's color. If it turns completely red, your line will break. Once you've reeled it in completely, it'll prompt you with a direction such as up, down, left, or right with the WASD keys or the joystick, if you're using a controller. If you react by hitting the correct direction, the harpoon will come right out.
The whale will swim away and you must do this twice more. On the second harpoon, after reeling it in completely, it'll prompt you with another direction followed by a second button with your right hand that you only have a limited time to tap. The third harpoon will require you to hit several reactionary buttons with a limited time to respond as well.
Moonglow Bay Chapter 2 Boss: Subdue the Storm Fish
There's a large fish in Waking Storm feeding on the lightning due to the antenna on its head. After purchasing the right equipment from Abi, head out to Waking Storm. Here, the buoys are redirecting the lightning, but the fish keeps knocking them over.
The goal here is to catch the enormous fish, but if you successfully latch onto it with your fishing line, the lightning can shock and break it, so it's necessary to flip the buoys topside before attempting to catch the fish. It'll swim around in a circle, continuously knocking them over as it goes, so it's better to strategically place yourself in its path rather than follow it because it moves rather quickly.
It might take a few tries to get the timing just right, but once you're successful, the antenna will simply pop off, and the storm fish will no longer be wreaking havoc on Moonglow Bay's waters.
Moonglow Bay Chapter 3 Boss: Catch the Twin Fish
Once again, you and your daughter will say your goal is to catch the betta angel fish, but that's not actually what will happen here. When you make it to Twintail Lake in the new hidden area, you decide to separate the fish using the tall structure on the small island. In your dinghy, you'll want to get one of the betta fish to chase you by moving in front of it.
When you do this, you'll notice an exclamation point will pop up just before it juts forward to attack you. Don't worry -- nothing bad will happen if it hits you. Your goal is to destroy the formation on the island and to do this, you must get the betta fish to ram into the land formation three times. Either betta fish can be used for this. Steer in front of the fish while it follows you until you're positioned next to the island, then quickly move away so the betta fish rams into it. Rinse and repeat twice until the debris blocks off the water.
Moonglow Bay Chapter 4 Boss: Defeat the Kraken
This boss "fight" is the easiest of them yet. It turns out the Kraken is just a giant squid who's upset that his water is polluted. All you need to do is clean the water around the squid with your net. Occasionally, the squid will chuck blocks of ice at you, but they're easy to avoid. They won't land on top of you, only throw you off-balance for a few seconds and disrupt your cleaning spree.
Moonglow Bay Chapter 5 Watermills: Free the New Species
Unsurprisingly, you decide that the beast needs to live free rather than be caught. You'll pull a lever to open the gate so it can leave, but the watermills need to be running for it to open. When you pull the lever, a timer will start, giving you eight minutes to start all 15 watermills, but it's plenty of time.
You'll start on land, so start with the four nearby mills on foot. Cast your line out to the wheel when it's highlighted in a white outline and pull back on the rod, which will get the mill moving. Then, get in your boat. You'll have to follow the wind current (see the map above for the most efficient order), so hop over the four mills you just hit and start the two in front of you (#2), followed by one on the right (#3).
You'll follow the peninsula around in a sort of counterclockwise direction. On the right side of the map, you'll hit one on the left (#4) and two on the right (#5). Navigate north to Sparkle Tide and get those three of varying sizes (#6), and U-turn back in the direction you started toward the west. One will be on your right (#7) followed by one more (#8) just before the wind takes you back over to Floating Stones. At this point, a cutscene should commence, indicating that you were successful.