Then the goblin's eyes go white, and you feel a psychic explosion fill your brains, rending your synapses.

Everyone: make a DC 13 Intelligence saving throw. (At disadvantage if you failed the CON Save.) On a failed save, take 10 psychic damage and become incapacitated until the end of the goblin’s next turn. On a successful save, you take half as much damage only.

Everyone who is not incapacitated may act, following your two saves.

Instantly, Bryony hits it in the shoulder with her arrow, wounding it.

Everyone who is not incapacitated may act, following your two saves.

Jurgen Saves:

CON: 11

INT: 23

Jurgen will examine the stairway and the west hallway, without going down either. 

Bryony Con Save: 10 (I believe she still makes it?)

Bryony Int Save: 19

"Why did you do that?" Bryony shouts, her head ringing with pain. "Stop it right now!"

She runs up to the goblin and attacks with her blades.

Shortsword: 18 to hit for 5 piercing damage

Dagger: 25 to hit for 5 piercing damage

Fergus Con Save: 14

Fergus Int Save: 3

Blinking, Fergus is momentarily stunned.

Jurgen gets a glimpse of a mess hall to the south- stone tables and benches, and gets a fragmentary glimpse of at least two goblins, although it certainly sounds like more in there, as the chaotic sound of alarm spreads. To the northwest he sees a narrow circular staircase leading upward. A few small colored beads are scattered across some of the steps. Then he steps into the immediate fray, swinging and missing.

Fergus freezes up.

Bryony manages to injure the overwhelmed, shouting goblin who is trying to bar their entry.

Quinn and Boona may roll those saves, then act if not incapacitated.

(Don't forget to mark those 5 psychic damage if you made your second save, and 10 if you didn't!)

Boona

DC 10 Constitution saving throw 25

 DC 13 Intelligence saving throw 14

Boona doesn't even notice the gas and her mind is a little too smooth for the mental attack to stick, she moves up and noting her companions in pain swats at the goblin.

Attack: 20 Damage: 11

Boona manages to clobber the strange little goblin. It looks bloodied, but it's not yet backing down. It continues to scream for help in Goblin.

From the east stairwell, Laiti appears and looks around. She points upward. "The guy needs help. Upstairs." 

Quinn may go next!

Con save: 24 (Nat 20 + 4)

Int save: 5

Quinn uses his guarded mind feat and automatically succeeds the ain’t save.

Con save to remain concentration on Pass Without Trace: 11. Success!…barely. 

Quinn rushes to silence the goblin. He throws his dart at it and then follows up with by smashes it with Lightbringer. 

Move: Run into melee range

Attack 1: 20 to hit for 5 damage. Target is Vexed and Quinn has Advantage on next attack. 

Attack 2: 23 for 10 damage (7+3 from colossus slayer). Target is sapped. It has Disadvantage on next attack

Note: Due to Mage Slayer feat, if the goblin is concentrating on a spell, it has disadvantage on that Con save. 

Quinn pounds the little goblin, twice. It's in bad shape.

Jorzu appears, staggering down the east stairwell. "Arrrgh!" Half-crouching in a defensive stance as he retreats backward down the stairwell, Jorzu looks near death. "Help. Help. Help..." he chants over and over as each foot hits a step. 

A second strange goblin appears, chasing Jorzu down the circular stairs, slashing at him again and again with a ghostly blade made of pure psychic power.
Psychic Blade Attack #1 vs. Jorzu: 13. Hit: 9 psychic damage, and Jorzu must subtract 3 from the next attack roll or saving throw he makes before the end of the goblin’s next turn.
Psychic Blade Attack #2 vs. Jorzu: 10. Hit: 13 psychic damage, and Jorzu must subtract 4 from the next attack roll or saving throw he makes before the end of the goblin’s next turn.
Psychic Blade Attack #3 vs. Jorzu: 19. Hit: 9 psychic damage, and Jorzu must subtract 2 from the next attack roll or saving throw he makes before the end of the goblin’s next turn.

The first goblin, sapped from Quinn's assault, is soon reenergized by the appearance of his comrade. It conjures a second psychic blade, which it turns upon Quinn.
Psychic Blade Attack #1 vs. Quinn: 16. Hit: 8 psychic damage, and Quinn must subtract 4 from the next attack roll or saving throw he makes before the end of the goblin’s next turn.
Psychic Blade Attack #2 vs. Quinn: 20. Hit: 10 psychic damage, and Quinn must subtract 1 from the next attack roll or saving throw he makes before the end of the goblin’s next turn.
Psychic Blade Attack #3 vs. Quinn: 25. Hit: 7 psychic damage, and Quinn must subtract 2 from the next attack roll or saving throw he makes before the end of the goblin’s next turn.

More goblin faces - curious, alarmed, and confused - peer around the corners from the south.

(Jorzu goes down, I believe.)

Everyone may act!