Noell, seeing the Yuan-Ti man, reminds herself of the plan and aims her crossbow at him, firing before he can see the group approach (so long as he's not asleep.  I'm assuming Hayeth's burst was centered around the cultist raising the dagger for the stabby stabby, though, and not this guy.  If not, she's firing on anyone who is closest and *not asleep*).

Attack: 16 (with advantage from surprise)
Damage: 7 piercing

Initiative: 30

Dumasz hums a short lullaby rhythm, casting sleep 28 

initiative 4 

Lia will wait for Vahorn to send his first arrow or spell into the room, then assess the situation in the room. If all of the cultists appear unconscious, she'll run over towards the drugged man and attempt to carry him out of the room. If the woman with the dagger is still conscious, Lia will move to attack her. If not, assuming Vahorn casts entangle as discussed, she'll go for one of the cultists affected by that. If that also doesn't happen, she'll attack one of the yuan-ti.

If she finds a suitable target, she makes three attacks in quick succession - staff to the head, elbow to the throat, and knee to the crotch (flurry of blows).

Attack: 8 Damage: 8 (extra attack roll in case of advantage from entangle: 24)

Attack: 8 Damage: 5 (extra attack roll in case of advantage from entangle: 17)

Attack: 7 Damage: 6 (extra attack roll in case of advantage from entangle: 22)

Initiative: 4

When you all see Hayeth and Dumasz casting, you hold back your actions to allow their magic to resolve. The twinkling dust of sleep covers all the enemies.  All the cultists fall down, unconscious. The one in front drops her dagger as she falls, her hood falling back to reveal a pretty young woman with curly brown hair.  The two yuan-ti hiss as the rest of the party attack.

[[to be continued in a minute or two]]

As the Cultists fall, Vahorn looses his arrow at the Yuan-ti man. Attack: 9 Damage: 6 plus favoured foe 3

(second roll for surprise advantage? 9)

initiative - 11

Noell and Vahorn strike the humanoid Yuan-Ti, bloodying him. while Lia runs in and pulls the intended victim to safety.

Noell is up, followed by the Yuan-Ti.

Noell aims her crossbow again, hardened by the sight of the human sacrifice, and aims to kill the yuan-ti.  She lines up her crossbow carefully, and tries to hit a vital organ as she squeezes the trigger.

Attack: 19
Damage: 13

The male Yuan-ti is gravely injured, and leaps up onto the stone, charging Dumasz. he swipes at him ineffectually with his scimitar. The snake bodied Yuan-ti pulls out a longbow and looses a shot at Vahorn and Noell, but misses.

Okay, both enemies have taken their turns, so now everyone in the party may take a turn.

Ducking away from the snake-woman's arrow, Noell raises her crossbow and returns fire.  "Take care of the injured one!  I'll distract that archer!" she yells, moving behind what cover she can find as she tracks the snake.

Attack: 21
Damage: 12

Vahorn glances into the room, sniffing at the air. Drawing back the string of his longbow, he circles around Dumasz, getting a line of sight on his prey before firing at the previous wound on his neck to finish him off.

Attack: 10 Damage: 9 plus 2 

Vahorn gestures to the other Yuan Ti, “Take her down, then we can tie up these scum before they wake.”

Hayeth looks around the room and raises a hand with palm facing upwards towards the less injured of the Yuan-Ti once again the pages of her spellbook turn by themselves and she speaks arcane words her eyes turn a pale shade of blue and sparks of electricity arc between the strands of hair which stand up a little as though she is in a lightning storm and from her eyes into the air as a crackling orb of lightning appears in her hand and races towards the Yuan-Ti as she casts Chromatic Orb

Attack: 21 Damage: 15 (Lightning)

Dumasz grips his longsword in both hands to execute the yuan-ti before him. “Your plans are finished!” 
Attack: 17 Damage: 10 

Lia props the would-be victim against the wall, then rushes back in towards either of the yuan-ti that's still standing and makes two strikes against them.

Attack: 15 Damage: 7

Attack: 15 Damage: 4

Lia and Dumasz see the yuan-ti shift into a snake and try to slither away. They both successfully strike out it for 5 damage each, but it gets away from them and is right next to a crack in the wall.  [[Rolled your OAs for you.]] Party is up

As the fallen Yuan ti drops to his knees, Vahorn runs up to him grabbing the arrow embedded in his throat. With his foot on his chest he pushes him to the floor, freeing his arrow as he notices the snake slither towards the crack. 

Turning to the crack, he reaches his hand out as a soft, melodic sound comes from his mouth. “Ó, a Fhoraois mhór, cuir bac ar an éalú seo.” From the crack in the wall, barky tree roots, vines, shoots, and prickly stems come forth, spreading into the room. They grow around the snake squeezing tight to hold it in place.

Cast entangle centered on the crack, trying to catch the snake on the edge of it so my teammates can reach it - DC14 Strength saving throw or be restrained

For those who speak Sylvan 

Noell's eyes nearly pop out of her head as she watches the woman transform into a snake before her.  Quickly, she raises her crossbow and tracks it across the room.

Attack: 16 to hit, with or without advantage
Damage: 5

Cursing as her arrow flies less than true, she runs towards the crack in the wall, trying to block the snake from getting through (and using Misty Step to get through if the difficult terrain makes blocking the crack outstrip her movement speed, in such a position as to have the snake provoke an opportunity attack from Noell if it tries to flee).  Once there, she drops her bow and pulls out her rapier, brandishing it.

"Friends I think we need to fell this one, I fear it has our quarries mind in its grasp" Hayeth shouts out before saying "Shard meddwl shard o fy" as her eyes flash violet alongside a similar pulse of light from her hair spilling down her back as she casts Mind Sliver

DC 13 Intelligence Save

Damage: 2

But more importantly if he fails hopefully it takes the Negative d4 to it's save vs Entangle depending on order and if it fails

Lia tries to clamber past the vines to catch up with the fleeing snake, striking towards its head with the end of her staff, then stomping onto its spine.

Attack: 9 (with or without advantage) Damage: 10

Attack: 12 (with or without advantage) Damage: 5

Dumasz will try to grab the snake by it’s tail and pull it back into the room

athletics 18 

Noell's bolt damages the yuan-ti, but it is Lia, bounding across the room and striking with her staff that ends the combat.

The room grows silent.