Walkthrough: Underground Reservoir

Welcome to the murky depths of the Underground Reservoir! This area introduces new challenges and valuable items. Be prepared for aquatic enemies and platforming over water. Your goal here is to navigate through the flooded passages and eventually find a way to drain the water to access new areas.

Navigating the Initial Chambers

Upon entering the Underground Reservoir from the Castle Corridor, you'll find yourself in a large chamber with water. Your primary enemies here will be the Merman, who shoot projectiles, and the Fish Head, which are stationary but can be annoying. The Merman Soul (Bullet Type) is excellent for ranged attacks, especially against other aquatic foes, so try to acquire it.

Head right from the entrance. You'll encounter several Merman.
Continue right, dropping down into the water. You'll need to swim.
In the next room to the right, you'll find a Potion on a small ledge above the water. Grab it.
Proceed further right. You'll come across a vertical shaft.

The Vertical Shaft and Hidden Passages

This vertical shaft has multiple paths and hidden areas. Exploration is key here.

Going Down: Descend the shaft. You'll encounter more Merman and potentially Fish Head.
Left Path (Bottom): At the very bottom, take the path to the left. This leads to a small room containing a High Potion. Be wary of a Merman guarding it.
Right Path (Bottom): The path to the right at the bottom of the shaft leads to a dead end for now, but remember it for later.
Mid-Shaft Exploration: As you ascend or descend, look for ledges. There's a hidden passage on the right side, roughly halfway up the shaft.
Hidden Room: Enter this hidden passage. It leads to a room with a Whip Sword! This is a powerful early-game weapon, so equip it.
Continue Up: Once you've explored the lower sections, make your way to the top of the vertical shaft.

The Water Control Room

At the top of the vertical shaft, you'll find a crucial room that controls the water level of the reservoir.

Head right from the top of the vertical shaft.
You'll enter a larger chamber with a mechanism. This is the Water Control Room.
Defeat any Merman or other enemies present.
Locate the lever or switch in the center of the room. Activate it. This will drain a significant portion of the water from the Underground Reservoir, opening up new pathways.
After activating the switch, you'll notice the water level has dropped.

Post-Drainage Exploration

With the water drained, new areas are now accessible. Retrace your steps to explore these newly opened paths.

Return to the Vertical Shaft: Go back to the large vertical shaft you just navigated.
Bottom Right Path: Remember the dead end at the bottom right? It's no longer a dead end! The water has receded, revealing a new passage.
New Area: Proceed through this newly accessible path. You'll find a room containing a Mind Up.
Further Exploration: Continue past the Mind Up room. This path will eventually lead you to the Study area, connecting the Underground Reservoir to the next major section of the castle.

Before leaving the Underground Reservoir entirely, consider revisiting any previously flooded areas to see if new items or paths have been revealed due to the lower water level. The Merman Soul remains useful for any lingering aquatic threats.