Deapite tbe howling winds, you notice the chamber smells strongly of sulphur. Also, the floor of this chamber is strangely clear of sand and debris.  

If the PC with detect thoughts get within 3pft ir if anyone gets within ten feet, you hear the armored woman say "Quickly, this way! We can fight them together!" as she beckins them into the room where the rogue already stands.  All see her gesturing to be understood over the strong winds.

 Edit: sorry, just saw I put ⏸️ for Kandalou, in error. Should have been ▶️

Wizard moves toward the armored woman.

Quadere (Cleric)

(Quadere will scoop the brooch and keep it)

Attack on Mindflayer: Sacred Flame 16 Dex save 16

Before I move out-of-sight

Firebolt to mind flayer: Attack: 16 Damage: 14

Quote from BlueBayou >>

Quadere (Cleric)...

Attack on Mindflayer: Sacred Flame 16 Dex save 16

 He's stunned for the moment, so he fails that automatically.

<I know the initiative order says otherwise, but this is how I run initiative, these things are happening simultaneously as outlined in Xanathar's, so if the cleric prefers (and I presume this to be the case) sacred flame to take effect before the stun wears off, that is what happens.>

Note: I moved the cleric's position, but did not change initiative, to reflect the fact they grabbed the brooch.

Ven casts faerie fire on the illithid and its thrall before retreating toward the woman beckoning.

DC 15 dex

Duergar dex save 10

Illithid fails automatically (with advantage!)

Quote from Bjorn_Stahle >>

(OOC : Note for our missile users - Against prone creatures, Missile weapons have disadvantage to hit, BUT Vishnu will be able to go before my turn so he will be able to attack the MIndflayer while it's still stunned with his bow, so Advantage/Disadvantage cancels out and he gets a normal attack with his bow, if he chooses... )

Shaiere will normal attack the downed Mindflayer with Advantage twice, a third time with my bonus attack (Note Rollling advantage seperately because I don't trust the way the dice roller does it)

Attack 1 23/9 Damage 8

Attack 2 18/18 Damage 5

Bonus Attack 3 10/22 Damage 9 (No KI for any specials)

 Did you want to update this if the grapple contest succeeds? 

<multiattack should allow for 2 attempts, but if it fails, the second attack is just with the knife>

Vishnu (rogue) is also still up.

Here's the map with the lighting from the wizard and clerics spells. The rogue is in the dark, but will be lit if in the hallway.

<I was going to add the faerie fire to the monsters, but wanted to ask what color it should be (player's choice).>

The woman is backing into the room, wizard approached 30ft (movement limit)

<for you metagamers, I am keeping track of monster hp. Mindflayer has taken 75 damage.  He's still alive, though.  I roll hit dice for some monsters, so sometimes they'll go down early, other times they last a little longer.  This is the only roll I do 'behind the screen,' so to speak. The duergar has taken 5, btw. >

I’ll cast message on the Fighter, “gather the others and retreat with us!”

(Reminder: fighter, bard and rogue have Bless on them)

I was holding for the monk, but I can actually bifurcate this pending resolution.  If he fails the grapple contest, (duergar thrall: 21) Shaiere ends up on Toril, on success he can act per original post, on failure a new course of action.

The mind flayer recovers geom his stunned state and sees  giths standing before him.  He unleashes a psychic blast, (60ft cone) bathing Quadere, Kandalou, Vendelen, (and maybe Shaiere,) in painful waves of psychic energy.

DC15 Int save or take 22 psychic damage and stunned for 1 minute.

Intellect Fortress grants both resistance to the damage and advantage on the save and is still in effect.

<so, here's the problem.  If the monk succeeds on the grapple (and could, since the duergar rolled pretty poorly) that really would be enough damage to end the mind flayer.  So, this post only applies if the the monk fails on the grapple contest>

Quote from Wile_E_Coyote>>

I was going to add the faerie fire to the monsters, but wanted to ask what color it should be (player's choice)

<Some unnameable color on a spectrum only those that have experienced Limbo can understand... Humans would register it as an ultra-bright purple>

Grapple - Dex (+3) + Acrobatics (+7) check to resist 21 = 24

Shaiere resisted the grapple and therefore is in the mind blast effect. Int save : 6

Just 3 attacks On the Mind Flayer then.

Attack 1 22 Damage 5

Attack 2 13 Damage 4

Bonus attack 3 12 Damage 4