Bryony nods at Quinn and will join him in heading down the westward track.

Holding up Lightbringer and peering into the western tunnel, Quinn and Bryony can see track extending into the distance, sloping gently downward. (They presume the bad-smelling eastern passage by the lift probably goes somewhere below these tracks, but this tunnel might well connect to the track in the Crystal Cavern that Laiti described.

----

Meanwhile, Laiti nods at Fergus' explanation. She drifts over to the window to peer out at the pyramid in the the blue lava sea before heading back to the door and popping out of sight. The door opens, and Fergus spots a nervous goblin peering in from afar, before tiny invisible hands shut it again. Fergus and Boona are about halfway through their Short Rest. 

Laiti reports back to Jorzu.

Jurgen will advance up with the team to the east.

Jurgen catches up with the group on the tracks. His sharp kobold eyes can see further into the gloom than the rest of you; he spots a glint of purple light down the southwest track as he passes, and he can also see that the eastern tunnel opens up onto a larger chamber further to the east. 

"Maybe we should head back the other way?" Bryony says to Quinn and Jurgen. "This might just go to the bad-smelling place. I don't want to go there right away if we can help it."

Unless Quinn or Jurgen stops her, she'll change directions and head down the eastern passageway instead, using her light stone and walking slowly and carefully.

Jorzu 

Invisi-Jorzu matches stride with Byrony and says; "Don't forget about the crystal creatures. I wouldn't go barging into that room, if it is where these tracks lead, without a plan. Laiti wasn't too happy about those creatures." He will follow Byrony no matter which way she chooses to travel.

Bryony carefully heads down the eastern hallway, where the cavern opens up and the tracks turn abruptly southwest. Jorzu follows.

Bryony can see very little. Just stone and track, and maybe the hint of a wooden crate in the gloom ahead. She also sees, curiously, a small red flame somewhere to the southeast, like an obscured candle, or a pilot light.

Jorzu can see much farther through the darkness. He begins to take in some of the visible contours of this large cavern. He sees that stacks of crates fill this chamber. Some are half-covered by dusty tarps that barely hide the ore within, while others are nailed shut. He also sees a massive, conical iron drill, maybe 20 feet to the southeast. As he watches, its insides roar alight with a blazing red fire. Then it charges toward Jorzu and Bryony with a piercing screech.

Roll initiative!
Flaming Auger: 17

Everyone can hear the screech and see the flash of flame.

In the Overlook Forge above, Boona and Fergus also hear and see a sudden commotion through the hole in the eastern wall where the bucket conveyor exits. (With about 20 minutes left on their rest, they cannot participate in any fight without jeopardizing their Short Rest. That includes rolling or acting on initiative.) Boona, closest to the hole, can now see it's about a 20 foot drop to the cavern floor below. She gets a glimpse of the burning auger below and to the north.

Quinn follows the guidance of his friends and decides against moving further down the tunnel. He turns to look over his shoulder and then hears a roar down the tunnel where Jorzu and Bryony went. 

Quinn turns on his heels and heads towards the commotion.

Initiative: 18

DM: how far is Quinn from combat, both melee and ranged? I think I can reach the auger with Zephyr Strike that gives me 70 ft of movement. 

(Quinn can reach melee range with the huge construct in about 45 feet of movement, although he risks barrelling over invisi-Jorzu along the way. To reach line-of-sight ranged range, he would need about 25-30 feet of movement and remain just behind the front line.)

Fergus:

”Something is happening down there Boona—do you think our friends need our help?” asks Fergus.

He tries to get a better view of the goings on and determine if the scouting group is engaging whatever is making that light and noise, or if they are trying to avoid it.

Passive Perception:  13

Jurgen Init 7

he would move forward. 

Fergus and Boona can see that a massive auger, wreathed in hellish red flames, is shrieking to the northwest. (They cannot see the rest of the party.) They can also see the rest of the conveyor circuit for the buckets, looping near the floor of the cavern some 20 feet below. 

Meanwhile, Jurgen advances toward the front line.

Jorzu 

"Oh no" is all Jorzu has to say about the drill as its flames dance in the darkness.

Initiative 8

Boona looked out but shrugged...it was certainly colourful...

Initiative:

Quinn: 18 - Quinn may act.
Fiendish Auger: 17 - charging straight toward Jorzu and Bryony.
Jorzu: 8 (still invisible)
Jurgen: 7
Bryony: Should roll initiative and act on 17+
Boona and/or Fergus may roll initiative, but will lose their chance at a Short Rest if they do.

Quinn carefully navigates the tunnel unsure of what’s ahead. He sees a red hot glow flaring up and he picks up pace to check on his friends. He stops in his tracks as he sees the flaming auger shrieking and grinding its gears as it bears down on Bryony.

Unsure how to attack this thing, Quinn elects to try and create a distraction or help his friends evade this monstrosity. Quinn clips Lightbringer to his belt and reaches for some prepared spell components in his pouch. He utters an arcane incantation taught to him by his elders and a dense fog cloud forms between the auger and Bryony.

He shouts out to Bryony and the invisible Jorzu.

”Get out of there!!”

He then backs up into the tunnel to create space for anyone to run in.

Move: move down the tunnel towards Bryony. He stops just as he gets line of sight of the auger. He’ll use any remaining movement to retreat back into the tunnel.

Action: Cast fog cloud in front of the auger obscuring view of Bryony and anyone else near the tunnel.

Thick, obscuring fog boils out of the ether, cloaking the whole scene in inpenetrable cloud. Quinn backs up as far as he has the time to...

But the massive, hellish drill barrels forward, picking up speed as it goes, before slamming into Bryony. 

Flaming Drill Melee Weapon Attack vs. Bryony: 15. Hit: 15 piercing damage plus 5 fire damage. 

The auger then releases a witheringly intense burst of heat (Bonus Action). Everyone except Boona and Fergus: Make a DC 17 CON save, taking 14 fire damage on a failed save, or half as much damage on a successful one. (Quinn is just within the radius; Boona and Fergus just outside of it, although they certainly feel it. They also hear Quinn's shout.)

Jorzu, Jurgen, and Bryony may act. ...But first, make that save and see if you're standing. The auger is completely invisible in the flame-filled fog. 
Quinn: Make that save (and roll a concentration check to maintain the fog if you wish.)