Walkthrough: The Nino Ruins, Part II

You've just barely scratched the surface of the deep and complex Nino Ruins, and now it's flooded with water to make things worse. Equip those Hydrojets, or else it'll take you an eternity to get anywhere. Also, you can now jump MUCH higher, and you can pick up objects with the Lifter that were too heavy before.

First, get used to moving around underwater, then head north through the door.
First, I'll point out that you can now lift the marble blocks in this hall with the Lifter. Stack two of them on top of each other next to the red wall, then jump on top of it and then to the top of the wall.
You should be able to JUST grab onto the ledge. Pull yourself up and jump to the opposite wall.
You should land in front of some flame-spraying Gorobeshus. All they can spray now are bubbles. :-)
Go through the east door, and then south through the square-shaped hall, and use the elevator there.
Proceed north into the square-shaped hall. The Fish Reaverbots won't hurt you if you ignore them. Find a marble block nearby, pick it up, then go to the north. You should see a button in front of a strong current. Throw the block on top of the button to shut off the current and create a shortcut for later.
Now, head east and use the elevator there. You'll be in a room with two control panels. You can download item data from one of them, and the other one lets you drain the water. Use both, then head back to the elevator and into the square-shaped hall.
The water's gone, and the fish are all helplessly flopping around.
Drill through the west wall, travel through the square-shaped hall, and go north.
You'll find another current machine, but you don't have to worry about it since you drained the water. Now, open the chest on the west end of the hall for 20,000 zenny. Now go north again into a double-square-shaped hall. There'll probably be a lot of Reaverbots blocking your way, but don't worry about them, and go through the northeast door.
Another crumbling wall to drill through. Same old, same old, head east.
Boss time! Three Jellyfish Reaverbots. These are the guardians of the Nino Ruins. Some guardians; without water, they can't even move. All they can do is shoot slow-moving energy bullets at you. Circle and shoot works, but...
The easiest way to do things is to just run up to one of them and drill away. They'll all be done for in NO time. When they're gone, take the Water Key 1 left in their wake and head back west.
Go south in this hall this time and you'll come to a room with a few Shark Reaverbots flopping around. Normally, they'd be dangerous, but without water, you can just run right past them. In this square-shaped hall, go east and use the elevator again.
You'll be back in the room with the control panels. Use the orange one to flood the ruins again. Back to the briny deep with you! Take the elevator back down and head north through the current machine you shut off.

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Backward: Nino Ruins, Part I
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Forward: Nino Ruins, Part III