"It sounds like some of your allies are in the watery pits.  Are you proposing a rescue mission?  If so we should prepare if anything.  We have items of magic and power found here maybe they can be of use?  Could you determine what they are, if they are safe and if they would be use in an upcoming battle?" Grenk questions.

"Well we should rescue our friends as soon as possible and get them to safety and once done we can figure out what we are doing from there." Mal says.

You hear some muffled sounds coming from through the secret door.  Eventually a voice speaks through the door in a thick gutteral language.  Mal, you understand the Draconic language, "Master, your servants have collapsed. Is everything ok?  Master?"  There's a bang on the door. 

Sickle crawls back out of the hole where he had shoved his head in, dusting off a wriggling pouch he had grabbed from the nearby pile of goods.

“The triangle...his servants...perhaps his undead...died. Grab this person, force them to help us release our friends, and maybe we can escape through the harem or something. Or just skip grabbing this guy...”

”I could make a big ice snake that will grapple him and bring him in...”

Mal whispers, "Bad guys incoming be ready." Then she will hide next to the door and wait till the last one enters, and will strike at the one first.

Stealth: 26 (Add =10 to the roll if the Pass without a Trace spell is still active.)

"Can someone talk like that guy?" Silas whispers as he looks for a hiding spot, "Get him to come and we ambush him,"

In an ironic twist, Badger will cast Animate Dead on the dead necromancer's body, raising him as a zombie. He will then have the zombie stand by the door. Perhaps Mal can speak Draconic and hope the sight of their leader will be enough to convince them...

"I can try and pass myself off as him, but I have never heard him speak so I truly have no idea what he sounds like." Mal whispers.

“Just say...’Acerrrrerrraaaakk’”

Just cough and wheeze a lot

^--- LOL.  Give yourself some inspiration.  Heck, everyone please assign yourself some inspiration for excellent roleplaying thus far. 

Ok, so, Badger, your animate dead spell is probably not going to work due to the three horrific wounds on his body and the blood everywhere.  Maybe if you had 30 minutes to fix him up.  And, quite right, Mal can speak their language but is a woman and not a big snake dude and has never heard his voice it's impossible for her to imitate him.  

But, as you're trying to sort all these ideas out (and have the big snake body stood up and near the door), the door pushes open and a snake torso'd warrior barges in.  He does not have a weapon out.  He stops, looking at the undead creature standing before him covered in blood.  In Draconic, "Are....are...are you ok?"  His eyes dart around room to everyone here....

Roll initiative. 

Snake guy init: 7

Badger Initiative: 17

Badger's a little jumpy after seeing all the horrible stuff in this place, and the spell leaves his lips almost without thinking...

Chromatic Orb (1st level): Attack: 10 Damage: 11 lightning damage

Sickle Init: 10

Ice sprays from Sickles hand forming into a Giant Constrictor Snake

Ice Snake Init: 14

Bonus Action: Shillelagh

(Can the snake go this round? If so, then going for constrict attack)

Grenk initiative 21

Grenk just calmly strides forward, fancy sword in his hand and gives it a thrust at the Yuan-Ti.  He then pulls back and slashes.

Attack: 15 Damage: 7

Attack: 19 Damage: 9

Mal initiative: 24

Scimitar #1: Attack: 22 Damage: 11

Scimitar #2: Attack: 20 Damage: 11

Sneak Attack Damage: 5

Silas: 14

"Do not fear, you will be joining him soon," Silas casts Sacred Flame at him. 

Dex Save: 14

Damage: 15

Dex save: 3 (Silas, what spell, i only see "tooltip not found") 

Mal's as fast as liquid and slips forward her scimitars slashing into the snake warrior.  He moves quick, attempting to avoid and only his practiced skills prevent the blows from being killing blows, instead taking glancing slashes.  The magical long sword in Grenk's hands is slightly red tinged along it's steel length as his first blow slashes the arm of the creature lightly though it mostly dodges.  A ball of lightning flashes past and lightning courses through the creatures body.  A spell from Silas flits past and slams into him. 

A massive ice snake begins forming before him. 

(OOC: The creatures goes at its initiative.  If its initiative is less than it's caster, then it attacks in the same round, if it's higher than the caster, then it is next round.  Either way, the creature will act before it's summoners next turn.  In this case, it will be next round, and this snake creature will get to react before it can attempt to constrict him.)

The large warrior is still very much alive, despite the sudden onslaught of attacks.  His scimitar whips from it's sheath, and he attempts a fighting withdraw..****y pausing long enough to watch Sickle's outstretched hand spraying ice into the shape of a large snake.  He seems...mesmerized by that and looks up, making note of Sickle's face, before he backs away and then turns and runs.  As he does so you hear, "RAISE THE ALARM!!  RAISE THE ALARM, ASSASSINS IN THE RAS NSI'S ROOM!! ASSASSINS!!!"  (he moves 30 feet away around a corner). 

Next round, Mal is first. 

If I get one AoO Scimitar: Attack: 24 Damage: 6

"Not so fast!" As Mal chases him down continuing to attack.

Scimitar #1: Attack: 19 Damage: 8

Scimitar #2: Attack: 11 Damage: 11

Mal charges after him, out into the next room.  (He disengaged for his turn, so no AoO.) 

Four pillars support the vaulted ceiling, and steps ascend to an iron throne carved in the likeness of a hydra just to your left. Painted on the wall behind it is a large blue triangle. To the south, an engraved stone disk is set into the floor of an alcove that matches the teleportation pad in the previous room.  A ten-foot-wide opening in the east wall leads to a flooded cave. A ten foot wide passage leads away in the west wall to some double doors. 

There are four undead forms collapsed on the floor here, along with three yuan-ti figures that all turn at the yell of alarm.  The warrior you're chasing has turned right and is running down the hallway, he managed to get just around the corner.  Mal runs to the corner and attacks, slashing him once. 

Three new bad guys go at: 10

Badger, your turn, then the 3 other snake folk will go. 

I've added the entrance tunnel that you saw going into the ground to the map so you have a sense of scale.

Badger runs into the room, realising that he has seen it before although from the opposite side. Recognising the three yuan-ti in the room, Badger conjures images in their minds of their deepest horrors, as their zombified master appears behind Badger.

Move 25' next to the closest pillar, then cast Fear toward the yuan-ti.
Bonus action: command the zombie to pursue the three yuan-ti.