Where Bowser’s underwater castle resides, and, ultimately, the thing standing between you and saving Peach once and for all on your watery escapade.

Being even further down than Crepuscolo, the Anguilla Trench is situated in some of the deepest depths of the ocean. It’s so deep in fact, that no sunlight hits the trench at all, enveloping most of it in an ominous cloud of darkness. So, instead, scant amounts of light are provided by the bioluminescent fauna that reside in the trench’s depths.

Unlike the previous locations you have explored, which may have been a great harm to you due to military activity, pollution, or mass genocide, Anguilla is harmful due to none other than Mother Nature herself. You can’t really trust the uncanny creatures that live shrouded in Anguilla’s dark waters. You’re foreign to all of them, so they’ll surely be out to get you. In fact, the trench gets its name from the oddly frightening unagi eels that you first encountered in Jolly Roger Bay that also reside here… in much larger numbers, too.

Besides, some deadly currents and volcanic vents also exist in and around the trench. Bowser decided to construct his submerged castle in the Verme Volcano, a giant underwater volcano located at the edge of Anguilla. This is the only part of the whole trench that receives considerable illumination, and that’s only because of the vast amount of volcanic activity that’s so hot, that it brightens everything around it. Considering how many of his past castles were located in volcanic environments on land, Bowser thought that situating his castle in a volcano once again, albeit underwater, would give him a better chance at succeeding.

This is truly the darkest part of your journey. Survival may be more convoluted than expected, especially when you’re not sure what’s in front of you or behind you. Several visitors and unwary fauna that have previously visited the trench had their lives sacrificed in a heartbeat. Will you be the same?

8-1 Currently Heading to Anguilla

At this point, you’re at the end of Crepuscolo, low enough in the ocean to where the water pressure is causing your vision to become duller. Crepuscolo and the Anguilla Trench are separated by a ravine with an immensely strong current. The massive amounts of jelectros, as well as much larger pink jellyfish, are resistant to the strong current, allowing them to swim about freely without being pushed by the current. Due to Jr and the Koopalings’ naval activity in Crepuscolo, the cheep cheeps that formerly lived there had to flock to this current instead, where they’ve had to try very hard to live while swimming against the sheer force of the current.

However, you don’t have the same biological advantages as the swarms of jellyfish that inhabit this ravine that partitions Crepuscolo and Anguilla, so you have no other option but to swim with the punishing strength and speed of the current. They say that many that have attempted to cross this current in the past have failed to Come Back to Earth.

As deadly as the massive force exerted by the ravine’s current already is, Bowser has also gone in and installed several naval mines near and within Anguilla, such as along the current. They’re not balloons. Don’t pop them.

The ravine’s bottom is arguably more deadly, as the strength of the current alternates the deeper you swim into it, to where you’ll have no other option but to flap in the water like a bird between two pipes at the current’s strongest ends.

8-2 Unagi’s Night Vision Nest

Now that you’re in the Anguilla Trench, the water has become truly dark. Your first hurdle in this obscured, mysterious trench is to get past a giant nest of unagis.

Since these eels live in complete darkness, they’ve been equipped with excellent vision to help them see in the blackened depths, as well as glow quite prominently in the dark. The unagis’ luminance may prove quite useful when swimming through their nest.

Their brightness helps them a lot with spotting potential predators that they need to hide their eggs from. Some of the unagis’ eggs are buried within the ground, but others have been laid out in the open within the nest. Touching these eggs won’t hurt, but their protective coating is about as bouncy as Lemmy’s balls.

Living alongside the unagis are the jellybeams. Although usually blue, these usually bright jellyfish have formed a symbiotic relationship with the unagis, allowing the eels to use their blue bioluminescent fluid for their own personal use of defending their nest. As a result, these pigment-free jellyfish are white in color, and produce duller light.

But, be extra careful of the bigger unagis that reside in this nest! The smaller unagis tend to swim left to right, or in a similar square formation, but big unagis are ready to come out of their nest alcoves and chase you down for even thinking about messing with their eggs. They swim very swiftly, so escaping them may not be possible until the slender beasts lose interest in you. Nonetheless, being chased down by a big unagi is a truly heart-racing experience. Their jaws are strong enough to crunch through the walls of submarines with ease.

8-3 Marrowstem’s Osseous Tunnel

While the unagi nest was at least somewhat bright, this tenebrous tunnel of bones is a lot less luminous. It’s dominated mostly by snoodles, giant alien-like tube worms that were once believed to not even be native to this galaxy. But, bizarrely enough, they do live on Earth, deep down in the Anguilla Trench.

Since they aren’t close enough to the Verme Volcano to feed off its gaseous nutrients, these snoodles are forced to live on a calcium-rich diet sustained by the numerous fish bones that live in these skeletal depths. Due to deep sea gigantism, some of these fish bones are not only bigger, but also faster. Nonetheless, they still make the perfect snack for the sessile alien annelids dotted about. Although fish bones are plentiful within this osseous tunnel, the worms actually are not that picky with where the bones they consume come from. The snoodles in Anguilla have even been spotted devouring entire skeletons of whales who were unfortunate enough to believe that Anguilla’s depths would be friendly enough to support their immense weight, and need for oxygen.

Several more mines have been planted at these depths by Bowser. They’re masked by the obscure water, however, so you may want to pay attention to where things move to find any inkling of where the mines are at.

However, this tunnel is guarded by Marrowstem, a truly massive off-colored snoodle with an even more insatiable appetite for bone matter. They’re so enormous for a deep sea worm that they can not be viewed fully in the darkness, even with their fiery red body segments, and bloodshot eyes that show their sheer hunger to eat any bone matter they can find.

Marrowstem’s massive body segments are decorated with prominent warts. Could these be the colossal worm’s weak spots?

8-FC1 The Maelstrom Quad Quest

Upon defeating Marrowstem, and leaving their osseous tunnel, you’re greeted with a bright sign that tells you just what might happen to you the nearer you inch Bowser’s castle.

At long last, you’ve made it to the Verme Volcano where Bowser’s underwater castle resides. However, to make it much more difficult to approach the castle’s submerged courtyard, Bowser set up one last challenge before him: a long array of strong pipe currents, thrusting whoever dares to cross them into the painfully hot magmatic rock in the volcano.

That being said, there is a way to disable the currents. You'll have to explore the vast cavities of the Verme Volcano until you reach a switch at the top, which effectively clogs off all of the current pipes.

Tons of the rock in the volcano spews out hot gasses, making the waters around the volcano significantly brighter than the prior stretches of the trench. You can even spot the yellow glint of vents off in the distance in the hot, dark navy water.

Although it is bright, the Verme Volcano still proves to be quite a challenge to traverse. Many active hydrothermal vents dot it, intermittently spewing out hot gasses that are unsafe to the touch. It’s almost like there’s fire underwater.

Due to the abundance of gasses in this volcano, there are an abundance of snoodles here, too. However, they are actually quite well nourished by the gasses produced by the hot vents they reside by. As such, they’re actually quite faster than they were in the much darker portions of Anguilla. Also, while also capable of surviving in much lower pressure reef environments like in Rosa, lava lotuses grow within the volcano, too. The extreme heat allows their spores to spread more easily.

After an unusually long absence, everyone’s favorite dangerously delicious breakfast item, the roto discs, have finally returned. They’ve been installed into the depths of the volcano to make your quest to press the switch even more challenging, despite how formidable the volcano already was naturally.

And, only after deactivating the currents and meandering your way back to the start of the volcano, you can finally reach the castle doors. Be wary of the large steam geysers that erupt from the gaseous abyss of the volcano.

But, at long last, finally, you’re here. You’ve made it into the hall of the King of the Koopas. And, it would seem as if he's right there by the courtyard, waiting to break physics by shooting fireballs at you on the exterior of his watery castle. On a bridge marked with an axe, too. Just like old times. It’s almost too easy.

8-FC2 Bowser’s Nautical Finale

The very last challenge on your journey. You’ve now finally made it inside of Bowser’s castle. Lemmy, who was presumed to be dead after his suffocation in Crepuscolo, greets you at the front entrance.

Kamek is also there, flying about the halls to try to attack you. The axe bridge fight was simply a diversion to distract you from the much bigger plans that Bowser and Kamek had. Did you seriously think that getting to Peach would be that easy?

To begin the very finale of your long wet journey to rescue Peach, Bowser Jr is waiting to fight you one last time, his head completely exposed. You no longer get to fight him under the safety net of fresh air, for his arena is completely submerged in boiling volcanic water, and has a floor that not only shifts up and down, but can also shoot out bullseye bills. But, after Jr’s many failed plans to stop you, will his last ditch efforts prove to be successful?

If you do manage to defeat Bowser’s overly ambitious son in his aquatic arena, you’ll finally get to fight the fiery King of the Koopas for real. Kamek has readily revived him from the collapsing axe bridge from earlier, and is now ready to finally confront you for an actual final battle.

You’ll need to take advantage of Bowser’s brute strength and lure him into activating switches on the floor, so that the walls can open up and let you defeat him.