Can make an Intimidation check if you like, although no specific conflicts at this point. The duergar are hard to intimidate purely due to their strength in numbers, and the stone giant appears to be very chill and non-threatening, even friendly despite his lack of pleasantries.

(Was not meant as intimidation, more like a warning sign and declaration, that he is not the talker of the group)

Rhayna CON save: 19

Rhayna brings her palms together and slightly bows. "May the blessing of She Who Guides be upon you Stonespeaker Hgraam." Replies Rhyana in Common. She inspects the elaborate carvings at the entrance, but she resists the urge the take out her Journal and start recording it. (History: 19) "These are my companions. We came to check on apprentice Rihuud, and see how is he fairing. Perhaps if apprentice Dorhun is available, we would like to ask him some questions. You mentioned that you have been expecting us. How can we be of service Stonespeaker?" Rhayna tries to swat away the urge to record the carvings.

Con save 15 with adv 14 if the bad air is from  magical effects rather than just bad air.

Kaylyn remains quiet as they make their way through the city.  She pays attention to the path taken so they do not become lost.  Used to the attitudes of some towards her as a Half-elf she does her best to ignore the insults and jostling. 

Zeno Con Save: 18

Zeno takes a look around to see if they are being followed. Perception: 15

Congrats, your lungs are strong, and you all passed your CON saves. 1 Even Sarith passed. I don't think Stool needs to roll, as it doesn't actually breathe.

No-one is following as far as Zeno can see, although he knows these duergar can turn invisible. Outsiders are generally not allowed in this area, and the group would have been stopped by several guards, if not for their pins.

Even seated as he is, the head of the Stonespeaker is higher than even Sekkar's own. Hgraam speaks clearly but as slowly as the steady drip of water in cavern pools. He voice is not loud, but it brings back to mind the the sound of grinding of the rocks when the citadel sunk into the earth. Peering at Rhayna from black, sunken eyes Hgraam replies: Already you have been of service, human. Dorhun informed me of your assistance with subduing Rihuud, and I am in your debt. What would you ask of me?

Then seeing Rhayna's furtive distracted glances toward the cave entrance, he adds: Do you appreciate our arts?

(Hgraam's questions are open to all, not just Rhayna. Anyone can jump in this conversation any time)

"We seek information.   There are strange things happening here, wild magic perhaps.  Do you know if it's source?   We are also trying to understand the power structure here,  how a red dragon is in service to the king and yet seems free."

Kaylyn says. 

(After the answers to the above...)

Zeno pipes in and asks, "We've heard about some strange upheaval among the derro, too.  Something about the Gray Ghosts...do you have any knowledge of this group?"

Ah, the dragon. Hgraam then pauses in thought for so long that impatient Kastix wonders if the giant fell asleep, until he speaks again in his ponderous voice:

Before I answer, you must know that my clan has sworn fealty to the Steelshadow kings, and we have been loyal to that agreement for time beyond memory. Thus I will not betray the secrets of the king. But know this: the psionics of the Keepers of the Flame, though weak individually, are powerful in combination - powerful enough even to subdue the mind of a dragon... for a time at least. Eventually Themberchaud will grow too strong even for them. More than this I will not say. However, I assume from your insignia that they have recruited you for something? Perhaps to retrieve something stolen from them? Is that why you ask about the Gray Ghosts? I know of them, and although I do not know the source of the madness spreading through the city, I do not think they could have effected something so powerful. Perhaps somehow they merely facilitate it, like clearing the way for a rolling boulder they did not dislodge. Something else stirs in the Underdark, something evil. The rock itself cries in pain and horror, and a madness creeps from the blackest depths. Pay heed to the signs surrounding you. A cave with two faces. Rock devoured, and the land overgrown. The pebble believes itself flesh. The earth rejects its wards, and the tunnels shake in fury. By these portents, you shall know of evil's presence and of evil's face. This is what the stones tell me.

Joetaro remains silent, listening to the story and taking in the information about the Gray Ghosts. 

"Can you tell us more about the gray ghosts? I keep hearing the name but no meanings attached," Kastix asks. 

Rhayna happily records the carvings by the entrance to the cavern into her Journal. As Stonespeaker Hgraam speaks, Rhayna knows that she should pay more attention to what he says. She pays half attention to the information conveyed to her companions, but then she freezes at the sentence “A cave with two faces.” She closes her Journal, and turns to the Stone Giant. “Stonespeaker Hgraam. I am afraid to deliver you some bad portent. We saw the Prince of Demons while we were at Sloobludop. We saw the Demon Lord rise from Darklake, and I am afraid the Kuo-Toa village is no more.” Says Rhayna with a sad and grave expression. She then gives him a summary of their experience at the village.

In reply to Kastix, the stone giant says: The derro are a degenerate race - wild, erratic and full of hate. They live in squalor on the city's perimeter, with almost no leadership, so it is highly unusual that they should have organised themselves and other outcasts into an entire guild of thieves and murderers. Their objectives are unclear, but they appear to have a purpose beyond simple crime. To steal from the Keepers of the Flame and to avoid the capture of the Stone Guard requires exceptional resolve and insight. 

Then after Rhayna's revelation, Hgraam sits in thought for a few more long moments. This is grave news indeed. How a Demon Lord should come to be in the Underdark is a mystery with the most severe consequences. I must think on this information. But your coming here is as a tremor through the bones of the earth, and I would offer you a gift.

With that he booms out a call into the cave in the language of the giants, and a minute later a familiar stone giant appears. It is Dorhun, and he is carrying something in his hands. Hgraam turns to Rhayna and says: Human, I give you charge of this stonespeaker crystal. May it assist you in your efforts to solve this mystery.

Dorhun bends down and extends his hands, revealing a shard of quartz. It seems small in the hands of the giant, but as Rhayna takes it she realises how large it actually is, being as long as her forearm. Kaylyn senses that the crystal resonates strongly with divination magic.

Sekkar broke his "stone-faced bodyguard" attitude (and the grandeur of the gift-giving moment as well - religious aspects of the task were beyond him anyway) by asking yet another practical question: "Is something known about their magic? The two of them that we saw had shining blades, that they could make look ordinary again, and both assassins simply vanished into thin air."

The ridges above Hgraam's eyes rise as Sekkar describes the assassins he saw. Forak-Erach-Naek. The Empty-Scabbard Killers! He turns and looks at Dorhun who has a similar stony expression of disbelief, then turns back to Sekkar. What you describe is a duergar soulblade - a myth among most duergar, a tale told to scare children, but they do indeed exist. For centuries they have remained hidden, occasionally abducting duergar children with the psionic gift and training them in their mysteries. Like all dark dwarves they have the power to increase their size and vanish from sight, but they can also create blades of pure psionic energy. What their motives are I do not know, although some say they manipulate the power structures of the dwarven kingdoms through intrigue and selective assassination. If the Gray Ghosts are allied with the Empty-Scabbard-Killers, then we have far under-estimated them.

"If those "Empty Scabbards" are so powerful, they can hire your Grey Ghosts. Though, that would make them less powerful if they need allies." Demonstrated his political prowess Sekkar. "Or more? If they managed to control that unruly lot?" He lost his train of thoughts and decided he will never try to analyze political intrigues. One thing was clear, though - whatever it is, they had to deal with mind-controlling beings. The thing he resented the most. Still, there was one more question: "I get the manipulation part" (he did not but it did not matter either) "but what about second head growing? That is not mind control, is it? That's magic. Can not someone, I don't know, trace it to the mage who does those things?"

Kaylyn pondered the information given but was at a loss of how it all fit together.  There was simply too much they didn't know or understand.  She feared they were getting caught up in something outside their control and their efforts to escape the underdark had them involved in whatever was happening.  This was a bad time to be in the underdark, worse than any other time for one used to walking among the trees and feeling the warmth of the sun on her face.

"Something is at work to shift the balance of power here, and it looks to be effecting more than just Gracklstugh, it is effecting the whole underdark.  Which means the overworld is also likely in danger.  Demon lords should not be loose, even here in the underdark.  When did these manipulations in power that caused the second head to grow and other things start?  Was there some event we are not aware of?" 

"Too grand for my tastes, Instead of worrying about grand scheme, best to scale it down to what we can do about. I think that demon lord always had two heads anyways. Back to our scale,  we have Gray Ghost possibility with these Empty Scabbards. One 'influential' asking us to check out the ghost, another want us to check out assassin? You guys care more then me. Looks like it's all connected in this place and it's a mess we're about to enter," Kastix scratches his head before let out a shout of frustration.