Despite everyone calling it the North Labyrinth in the NA version, the location itself uses the name North Dungeon.

The area resembles the disused basement under Alunze, and has the same music. There are three main branches to follow. Two are interconnected in a way that makes the party keep going back and forth between the two to open more of the other, and lead to several treasures, including a ReGi Ring, a (cursed) Killer Sword, and a powerful Thunder Axe that no one in the current party can use. The other path has the majority of the real puzzles.

In one room, a staircase moves away when approached, but there's a sign on the wall to help.

The key is figuring out how the stairs respond to approaches from each side, and maneuvering them into the tile at the bottom that has only one way out.

Also, the idiom is a method to one's madness.

There's a sliding platform puzzle later on; each of the platforms in a 3x3 grid can move around, but only if they have an arrow pointing that direction (step on the arrow to move it), and only if there's nothing in the way. The party enters at the bottom left, and there are doors in each of the other corners. First taking the platform across to the bottom right, then crossing some pits with the Hook, leads to...

Shaggy's default name of ぴかぴか (Pika pika) roughly translates to sparkle, glitter, or shiny (Pikachu is basically glitter-squeak).

Shaggy, the light-elemental capsule monster, has low physical stats and high everything else, including GUT, which means sticking around more often. Though relatively poor at causing damage, Shaggy is also the only capsule monster that can heal party members. The healing starts out weak, improving as the monster evolves. Higher classes also bring some offensive magic, which tends to work rather better than the physical attacks.

Back to the dungeon... it's not difficult to reach the door in the top right of the sliding platforms room from there, and pushing four pillars onto a section of floor that looks different is good for a fourth Dragon Egg. After visiting the other doors in the order given here, getting to the top left door should be simple enough. On the other side is another puzzle, consisting of a 3x3 grid of tiles, some light and some dark. There's a sign on the wall.

The problem with using a Bomb here is that each blast affects not only the tile beneath it, but also the ones next to it. The fastest solution is to explode a Bomb on each of the tiles on the right side, plus the center tile and the top left tile. With that done, a platform rises to make a bridge.

Avoid completing the puzzle with a chain reaction, or the game may get confused and make the platform keep rising forever.

Down another flight of stairs and past a save point comes the amazingly simple puzzle of pushing a pillar onto a button to open the door.

Prince Alec and Josef stand in the next room, ringed by a section of floor that looks a bit odd. As soon as the party approaches them, the odd-looking floor falls away, leaving them trapped in the middle of the room. "Despair" starts playing, and Idura appears.

Tezar (テザー) is the spell for warping out of dungeons. As with many other spells, the NA version gives it a more self-explanatory name.

Idura summons some mummies to attack the party. They're quite flammable and not all that tough.

Idura summons some trolls. They're tougher, but nothing a few fireballs can't obliterate.

Yes, she's talking more informally again. As for what to do... I'd go after Idura directly, and I'm not sure why that doesn't occur to them.

A bass voice interrupts.

1-25 "The Strongest Man" plays as Heidecker walks into the room.

Translating kisama as "you" fails to convey the level of disdain and hatred it carries, but I can't think of anything else that would still keep the primary meaning, so we'll settle for all caps. Regardless, the NA text completely misses the point. Idura already knows and loathes Heidecker. That's why he's so furious!

He summons a small pack of monsters to surround Heidecker.

Heidecker slaughters the monsters with no apparent effort.

Idura teleports away. Heidecker steps on a switch that connects a bridge to the platform where the others are.

He walks over to the prince.

Heidecker leads Prince Alec and Josef out of the room, then returns to talk to Maxim.

Heidecker leaves.

That's when Heidecker comes back into the room.

The music fades out.

Heidecker leaves again.

My guess is she was about to say something like 一人の女として ("for myself as a woman") and go into how they don't appreciate her for herself. She strikes me as, on the one hand, wanting to be taken seriously and respected in what many would consider to be a job that's supposed to belong to a man, while on the other hand embracing her femininity and wanting other people to see her as a person, and even as a desirable woman, not just as the esteemed commander. There's no contradiction there, but too often women are expected to pick one or the other, if not have it picked for them.