She sticks a foot in to nudge the bag out.

It works! After the bag is claimed, the mirror evaporates. 

The next one has a couple of potion bottles, one orange and one green. 

Nudge nudge.

She’s able to get one, then the mirror evaporates.

In this manner she leaves a trail of miscellaneous valuables behind her, including a rod which, while not red, is inscribed with swirling patterns and radiates a magical aura.

Then, at the sixth mirror she looks into, her reflection has nothing by her feet, but she has a strange gleam in her eye. The mirror wobbles alarmingly, and then there’s a second Belmarniss in front of the first.

Belmarniss's party will not be able to understand the ensuing conversation.

"You -" says the mirrored Belmarniss.

"Read the sign."

"- okay, I remember writing it but -"

"But?"

"- pretty sure if I kill you I get to live and otherwise I die."

"Is that the only difference?"

"...may also have started out in just a generally horrible mood. I think that's all."

"So does it matter, then? If I let you take notes and I keep them -"

"You shouldn't have come in here."

"I don't like lots of what I do during adventures, that's not new."

"You should've made the ogre do it or, better, borrowed a zombie."

"- okay, not thinking of that is on me."

"You didn't try. You're getting lazy."

"I'm sorry."

"Call them in here, untie me, get your damn loot, and give me your notebook."

Belmarniss sighs. And calls, in Common, "I think it's okay."

Garrus comes over to untie them, scrupulously avoiding looking into any mirrors along the way. (He still unties Original Belmarniss first, just in case.)

Belmarnisses check the remaining mirrors.

Original Belmarniss can see treasures ranging from gemstones to a Wand of Fireball to an enchanted lute, and can collect them as she wills. Reflected Belmarniss cannot, and in fact does not even have a reflection of her own.

Reflected Belmarniss takes the notebook that isn't going to dissolve in an hour and writes.

Original Belmarniss offers Deekin the lute and the more liquid swag and keeps the wand.

"Ooh, Doss Lute," Deekin says happily once he's examined the lute. "Good if we encounter poison." The orange potion he identifies as a Potion of Bull's Strength, while the rod from earlier he identifies as a Rod of Lesser Quicken Spell.

He casts a considering look at Reflected Belmarniss, but visibly decides against saying anything to her, instead scribbling in his tome-under-development.

"What," says Reflected Belmarniss.

"Deekin considered asking for interview but decided against it. Sorry to bother Belmarniss."

Growl.

Eventually Mirror Belmarniss says, "I should recharge your fucking staff."

Original Belmarniss hands it over. Mirror Belmarniss dumps spells into it.

And, after exactly an hour has passed, her skin gains a mirrored sheen and she melts away, leaving a red rod where she once stood.

Jojo sighs heavily.

The only Belmarniss collects the rod, and picks up the staff again, and takes the notebook, and sighs, and heads back to the puzzle.

The party remains quiet as they insert the appropriate rods into the levers, pull them, and create a path through the center column of the bridge. On the other side, there's a stairwell descending deeper into the earth.

When they cross the bridge, there's a little magical fireworks show as the rest of the pillars dissolve. Garrus snorts. "I'm sorry, that was just- so completely inappropriate. Halaster is such an asshole."

"Thank you."

They descend the stairs in a less awkward silence.

The stairs terminate in a small chamber which has a very different aesthetic from the previous floor: less "ancient temple," more "ancient crypt". (Alright, it's not that different, but after a while spent in the same architectural style it feels like a significant change.) There's one door out; when Garrus opens it, they behold a much larger central chamber than the one on the previous floor, centered on what looks like a bunker, with a pool of water out front surrounded by four glowing pedestals.

There are some drow standing watch around the pool. "Should I shoot them?" Garrus whispers. "I'm shooting them, right?"

"Maybe they'll talk. A surprising fraction of encounters today have talked. You want me to poke one with Message, see if I get anywhere and doesn't give away our whole position right away?"

Jojo considers this. "Yes, I think we should," he says after a moment. "Perhaps they were conscripted by this Valsharess. Or perhaps they're... drow rebels, nobly opposing their kin?" He shakes his head. "Probably not. Still, we shouldn't kill them without giving them a chance to explain themselves."

"Could also be more than one drow country in here. Or religious divisions. Or they think we're above their pay grade. All kinds of reasons to avoid a fight." She casts Message and aims at whoever appears to be in charge. "Hey, what are you up to, why is that pool worth guarding?"

The apparent leader is, oddly, male; he's dressed in wizard's robes, and the women around him are holding identical crossbows.

He twitches slightly when the message goes through, and signs something to his subordinates, who perk up. One of them casts Darkness on their position. "Leads to the next level," he says in response. "Who is this? Come out so I can see you."

"Comprehend Languages. Message. You gonna attack me if I do that?"

"Of course not. We can have a free and mutually beneficial exchange of information."

"We can do that right where we are, I can do this all day."