Not seeing much through the cloud of smoke that appeared mysteriously out of nowhere for no reason, Dori could only go where directed. Following after Gargan, being pushed ahead by Yazara.

Sariel Phyll

Sariel follows suit hoping the fire doesn't get too out of control. "Only you can create door fires." Sariel says jokingly feeling the tension rising as with the fire. 

You proceed through the door and (I assume) close it behind you to keep the smoke contained.  You move into another hallway that immediately turns right.  It's just long enough to hold the lot of you, and ends in stairs that go up, and appears to open into an open room.  From ahead you hear arguing:

"The fire's going to get worse and that thing is still in there!  We have to get out of here!"

"Relax you fool, it's all stone down here, there's nothing to burn.  It couldn't even get across that room.  And that 'thing' moves at a snails pace.  Let it come .. it'll take an hour for it to get in here"

"Gods will both of you shut your mouths!?  We have work to do!  If we don't get this stone back, Xanathar will have us all killed!"

<Muffled screams>

Let me know if you want to change the marching order, and what you want to do.

Cloudfur

Cloudfur pokes Dori in the butt and makes kicking motions, points at the door, then smiles as he hops back and forth excitedly.

In far away lands, surrounded by nearly impassable mountain ranges that reach high into the heavens, blotted out by neverending snowstorms, deafened by thunderous roars echoing daily and avalanches that are a constant hazard. There lives a tribe of goliath unlike any other where one thing and one thing only drives them into a unquenchable thirst for battle. 

A poke... in the butt.

Feeling the prod to his hind quarters, Dori would quickly turn to see the bouncing cat and knew instantly what was expected of him. A single, massive hand pulling forth his battleaxe before rushing into the room ahead swinging at the first thing unlucky enough to feel the cold steel of his axe. 

Attack: 7 Damage: 6

Gargan

As Dori moves into the room ahead Gargan prepares himself to follow. Once Cloudfur moves in after the Goliath Gargan will also move into the room making sure to allow space for the others to enter. He would then send a Fire bolt in the direction of the nearest foe.

Spell attack roll: 21 dealing 3 fire damage on a hit, if there is an enemy.

Cloudfur

The tabaxi follows Dori through the door and casts at the nearest target

[Thornwhip: 12  Damage: 6 piercing]

Initiative:

Sariel 10

Dori 6

Sizan 4

Gargan 5

Cloudfur 5

Baddies are 13.  

Dori runs like a freight train into the room.  As you all get to the top of the stairs you see a large, rectangular room about 15' wide and 50' long.  Threadbare curtains line both walls, though there are entrances to several rooms to the left, and a pair of double doors leading off to the right.  At the fair end is a small raised dais with two sets of stairs leading up to it.  On the dais is standing a nightmarish humanoid figure in black robes, tall and slender, with purple skin and several tentacles extending down from his face where a mouth would normally be.  It is floating about 6" above the ground.  Beside it is a dog-sized creature that looks like a brain with legs and feet.  The figure is staring straight at you, and leaves you feeling as if he's looking straight into your soul.

Closer to you on one side of the room is a a muscular half-orc, also in black robes though much more dingy than those worn by the other figure.  He is standing with his foot on the chest of a human with red-blond hair.  Fire burns around the orc’s clenched fist, and his victim cries and squirms helplessly beneath him.  

Closer still to you, backs turned are another humanoid, and a dwarf with grey skin and hair.  As you enter they turn, and recognize the human as Krentz - the Xanathar leader from the Yawning Portal brawl.  At the same time you all feel a small piercing pain in your heads, as the tall creature "yells"  "Get them you fools - he is the one we need!", pointing at Renaer.

Dori runs up, looking for the nearest target and runs for the dwarf swinging his axe in a wide arc.  The axe cleaves across the dwarf's chest, leaving his armour damaged and blood pouring from the wound.  

 Sariel comes up behind Dori and after watching him eviscerate the dwarf and assessing the situation, he throws his arms forth casting Guiding Bolt at the robed half-orc holding Floon down.  The light shoots forth from his hands and vaporizes the half-orc, leaving his robe and other belongings in a pile on the floor.

Renaer pushes through up behind, draws his rapier and runs up silently to Krentz.  He swipes once across his arm, comes back with a backhand which Krentz just manages to duck away from, and then just runs him right through the chest.  Blood runs from Krentz's mouth as he slowly slides down the wall.  Renaer pulls his sword free, wipes it on the dying man's sleeve and turns to the two remaining creatures.

The tentacled creature floats down, towards the double doors.  You can see him carrying a small black orb.  He points to your group at the end of the room and looks back at the small creature as he floats through the doors.  They close behind him.

Zemk swings his War Pick at Dori, it hits but mostly glances off his armour delivering only 3 slashing damage.

The small creature on the other end of the room hops hurriedly up to Dori and swipes at him with his claws but Dori ducks out of the way.   However after doing so Dori you feel a strong presence enter your mind, almost as if it's rumaging around in it.  You'll need to make an intelligence saving throw.

Charging in the room, Gargan and Cloudfur launch attacks against the dwarf.  The fire bolt flies right over it's head and sails down to the end of the room, exploding on the brick wall.  The thorn whip extends forth but the dwarf manages to pull out of the way.

Back to the top, once Dori makes his saving throw.

Int: 4

(If I'm about to take damage from this can I use stones endurance? )

Stones endurance: 4

Dori the feeling of something intrudes on your psyche.  You take 7 psychic damage and your intelligence score is reduced to 0.  You are stunned until further notice, essentially standing there like a drooling vegetable.

(Not sure how that changes Dori, but at least now he won't be burning anything. Guess I'm out of commission guys. See ya at the end. 😁)

Dori, your Stone's Endurance reduces the damage to 3, but your intelligence is still 0.  Until it restored or at least increased to 1, you are unable to take any action.  You are not dead, you just have the mental capacity of a rock.  You could likely carry out very basic physical functions like standing, maybe walking (slowly, and with some guidance), or other necessary bodily functions.  

Sariel turns, hands still glowing and sends another Guiding Bolt towards the small creature, searing it for 13  radiant damage.  Renaer moves up past Dori, careful not to knock him over, with dagger and rapier in hand.  He takes a swipe with his rapier, arcing just over top of the brain tissue, but then catches it on the back swing for 9 damage, and then thrusts his dagger forward for 7 piercing damage, sinking it up to the hilt right in between the lobes.  The small creature shudders and collapses on the ground.

Zemk, feeling quite outnumbered at this point, flails wildly at Cloudfur with his war pick, missing and sinking the tip into the wall beside him, and then darts through in between Cloudfur and Dori, heading towards the same double doors the tentacled creature went through.  As he pushes through the crowd of you, Gargan, Cloudfur and Renaer all get attacks of opportunity.

Gargan and Cloudfur each swing their quarterstaves at him, Gargan hitting for 2 damage and Cloudfur just missing.  Renaer pulls back just after stabbing the brain dog and backhands his rapier into him for 7 slashing damage.  The dwarf just makes it to the closest door and starts to open it.

Cloudfur & Gargan up then back to the top!

Gargan

As the dwarf is attempting to make his way out of the room Gargan pursues him, keen to end the threat he poses and also to follow the strange and menacing tentacled beast that was clearly the greatest danger in the room.

If the dwarf still lives when Gargan takes his turn he will move up to the double doors then cast Chill Touch on him.

If the dwarf is dealt with when Gargan takes his turn he will move through the double doors and look at his new surroundings. If the tentacled beast is there and in range he will launch a Chill Touch on him.

(Spell attack 10 dealing 7 necrotic damage)

(Just for clarity it was the brain dog that hit Dori - not the mind flayer)