Out of sight (understandably not hidden), Syvis attempts to scramble up the side of the building to gain a better vantage from the roof.

Acrobatics: 14

If she gets to the top, she'll crouch and fire off another shot at Bloppblippodd. (If the archpriest has already fallen, she'll aim at the guard Rian attacked)

Attack: 8 Damage: 5

Nicholas fires a bolt at Bloppblippodd that makes contact before like Syvis, running to a nearby building for cover (-4hp [Total: -58hp])

Thodek invokes the power of Moradin, causing his warhammer to glow with radiant divine power. The attack makes contact, causing a large burn across Bloppblippodd‘s chest (-12hp [Total: -70hp])

Svyis attempt to scramble up the wall of a nearby home, but just as she is about to reach the top, a foot slips and you find yourself sliding back to the ground. Shaking the mistake away, Syvis tries to focus on Bloppblippodd again, but her crossbow shot goes wide, missing the injured archpriest.

NPCs are up! 

Jimjar turns to engage the Kuo Toa that Derendil had already injured, taking two shortsword strikes against it. (Attack: 15 Damage: 4) (Attack: 24 Damage: 9) Both attacks make contact, causing the Kuo Toa to cry out in pain before falling limp onto the ground (Dead).

Cailean the wolf attempts to bite Bloppblippodd with advantage due to pack tactics. (Attack: 13 Damage: 9) Cailean jumps, tearing into the archpriests chest (14 Original was 11) The wolf’s strength is too much, and Bloppblippodd falls to the ground prone (-9hp [Total: -79])

Rian continues his longsword assault on the Kuo Toa engaged with him. (Attack: 10 Damage: 5) But the attack goes wide, glancing off of the Kuo Toa’s armor. (Original attack roll was 9. Roll got messed up when I added Bloppblippodd‘s strength save.) 

NPCs continued!

Derendil rushes over to the Kuo Toa engaged with Rian, and makes two claw attacks. (Attack: 9 Damage: 4) (Attack: 20 Damage: 5) 

Kuo Toa are up! There are 6 of them, one injured. 2 go for Jimjar, 2 for Derendil, and two for Rian. 

Jimjar: (Attack: 22 Damage: 6) (Attack: 4 Damage: 3)

Derendil: (Attack: 10 Damage: 7) (Attack: 11 Damage: 2)

Rian: (Attack: 15 Damage: 7) (Attack: 23 Damage: 4)

The attacks all miss except for one spear, which catches Jimjar in the shoulder (-4hp).

 Ploopploopeen is up!

 Ploopploopeen raises his scepter, striking with it two more times, with advantage because Bloppblippodd is prone. 

Attack: 17 Damage: 4 + 16 lightning 

Attack: 23 Damage: 4 + 13 lightning

The first one strikes Bloppblippodd in the chest causing her to give a gasp of pain. Plooploopeen then raises the scepter again, and with a grim smile, brings it down on his daughters head. With a final scream and a squirt, Bloppblippodd’s head is liberated from her shoulders.

The battle around you freezes as they all stare at the now severed head that is slowly rolling into the depression before the altar. A blackish-purple blood oozes out of the wound, and begins to fill the area. Silence permeates the air except for the sound of now red water lapping against the docks of Sloobludop.

(Combat is now over)

What would you like to do?

Still needing a better view, Syvis finds a crate, table, flotsam, or an errant kuo-toa to step on and try to gain a leg up to help her into the roof.

Acrobatics: 25

Wherever she ends up (roof or flat on her back), she'll try to get a good look at the surface of the water (or if she can see anything beneath) to see if anything seems to be drawn to the recently-introduced blood.

Perception: 7

Voyage rushes and tries to grab the head before too much blood drips into the altar.

Syvis is able to successfully climb onto the roof of the nearby building and with your vantage point are just able to make out what seems to be dozen of shadowy animals flitting through the nearby water, feeding on the bloody remains of floating dead Kuo Toa. 

Voyage quickly runs over to the altar, picking up the severed head of Bloppblippodd, stopping most of the blood from covering the area, but a small amount still soaks through the floor.

What would you like to do?

Battle now over, Nicholas quickly moves towards the altar and tries to stop the blood seeping in by washing it out with water.

Thodek moves to stand behind Ploopploopeen, and shouts out in undercommon,

Kuo Toa begin to cheer in agreement at Thodek’s words and begin to raise their spear, chanting. However, another sound begins to rise above the burbling cries of the kuo-toa. The dark surface of the water about 500 feet away starts to bubble and begins to foam. A thick, oily tentacle bursts forth, followed by another. Then two monstrous heads break the surface, both resembling hideous, angry baboons with wickedly curved tusks. Both heads are attached to a single torso, and the monster’s red eyes burn with bloodlust and madness. The creature rising from the Darklake must stand thirty feet tall or more, with water cascading down its back and shoulders. Upon reaching its full height, the great demon throws back both its heads and roars! The Demogorgon is in the Darklake!

All the Kuo Toa around you begin to fall into some sort of a trance, standing deathly still, eerily chanting “Leemooggoogoon! Leemooggoogoon!” Ploopploopeen stands, his mouth gaping hanging open. “Wh... what is this? Run!” he yells “to the boats!” But it is to no avail. All except Glooglugogg stand rigidly incapacitated.

Everyone please make a DC 13 Charisma Saving Throw to avoid a bout of short term madness at the sight of the demon prince.

Other than that, what would you like to do?

CHA saving throw: 20

Voyage will sweat under her breath and hold her action to grab someone who falls incapacitated and then movement and bonus action (due to expeditious retreat) to Dash towards the boats.

Thodek charisma: 15 (Advantage roll for if this qualifies for Duergar resilience: 3)

Thodek will try and rally the party to head for the boats and shepherd them all that direction.

CHA save: 5

Syvis does whatever the DM dictates because she has a distinctive lack of charisma.

CHA Save 8
Using a Luck Point to reroll 10

Nicholas is driven to a short bout of madness by the appearance of the demon prince.

Syvis (9) Nicholas (50)

Both of you begin to feel a creeping sensation at the back of your neck. Syvis, you find yourself overcome by fear, and are unable to move— paralyzed in fear. Nicholas, oddly, you begin to feel an overpowering urge to eat something. You look down at the severed head of Bloppblippodd, and know that you must consume it! 

NPC Saves 

(Cailean: 17) (Rian: 15)

(Derendil: 15) (Jimjar: 21)

Madness

(Cailean:43) (Rian: 92) (Derendil: 81)

Both Rian and Derendil stand rigidly still like the Kuo Toa, stunned at the sight of this demonic entity. Cailean the wolf begins to whine before dashing back towards Sloobludop, obviously frightened.

Jimjar begins to dash after the fleeing wolf. “Go, grab a boat! I’ll get Cailean, and find the others. Meet me at the docks near the safe house.” He yells before disappearing into the narrow alleyways of Sloobludop. 

This bout of madness will last for 10 minutes. What would everyone like to do?

Compelled by his overpowering hunger, Nicholas picks up the head of Bloppblippodd and takes a bite savouring its taste.

Syvis, ever so nimbley, takes no actions and stays absolutely still and silent, crouched low on the rooftop. She's not hidden, but not obvious.

(Since Rian is probably the smallest of those paralyzed and the nearest to Voyage, she would grab and try and drag him towards the boat.)

Thodek would smack the head away from Nicholas and drag him away towards the boats.

(Assuming athletics? 16)

Voyage. Please make an athletics check to attempt to drag Rian towards a boat. 

Thodek is able to slap the now partially eaten head of the archpriest out of Nicholas’ hands before grabbing him by the wrist and pulling towards the boat. Nicholas, please make a contested Acrobatics check to attempt escape and go back for your meal.

Acrobatics Check 14

Nicholas struggles in an attempt to return to his meal, but is unable to break free of Thodek's grasp.