Kala shrieks with pain and anger at the quintet of glowing darts that strike her. She is looking very wobbly as she again tries to resist Zartan's pull. DC15 STR save: 10 

The guards hustle the unconscious but stabilized party official away into the crowd.

Kala, a look of panic and rage upon her face, races toward you. She raises her hands and releases a deafening arcane wave of thunderous force. (Zartan and Walt: make a Constitution saving throw. If you fail. take 11 thunder damage and be pushed 10 feet away from you. On a success, take half as much damage and you are not pushed.)

Walt and Aranor may act next!

(Sorry - That's a DC12 CON Save.)

Zartan CON Save: 17

(What's the DC Save for the Thunder damage?)

Walt’s con save = 14

Walt braces himself and weathers most the thunderous impact. He stands firm and calls out the datura “Kala! Stop! We are not your enemies, but we will not allow you to harm these people any longer. What they did to your mother was wrong. Let us help you!” 

Walt stands resolute in a defensive posture and activates his Archer constellation with a bonus action. A celestial glow flickers around Walt and his joints light up with the constellation of the Archer.

DM: Not sure how this is going to pan out, so I’ll give some conditional responses. Walt is hoping to deescalate by referring to her by name and her mother while also showing strength and power with his magical Archer constellation.

Persuasion check if necessary: 18

Walt readies the action to cast entangle.

 IF Kala flees or attempts to attack, Walt will cast entangle to try and stop her.

(Walt and Zartan stand their ground, only taking 5 points of thunder damage from her arcane blast.)

"And what do YOU know of MY mother...?" calls out Kala from across the wreckage of the carriage. She is clearly still violently furious, but seems to hold her attack for the moment.

Aranor and Zartan may act next.

Zartan casts sleep on Kala (27 hp worth - set so it only catchers her)

four 1's (give me a break)

Kala crumples, unconscious, to the street, whispering a barely audible, "Biza..." as she falls. She is now fast asleep on the cobblestones.

But then a cloud of smoke coalesces above the wagon. A skeletal face appears within. In a raspy, ethereal voice, it begins to speak.

"A curse upon the names of Amos Nir, Kit Mata, Solenn Avim, Nargis Ruba, and Massimo Ain. I, Proud Edun, condemn them to an eternal death. And I condemn all those who aid them." 

The incorporeal entity turns upon Zartan, lunging to grasp him.

Proud Edun initiative: 4

Walt and Aranor may act next, before the unnerving entity can attack.

One of the guards who dragged away the masked man in the carriage pushes back through the fleeing, panicked crowd, his spear readied. (The other guard and the unconscious man are no longer visible.)

Walt stumbles back at the sight of the skeletal apparition and draws his moon touched scimitar. He casts guided bolt and calls down a strike from the Archer upon Proud Edun. Walt moves backwards 30 ft towards Aranor.

Action: Cast guided bolt. To Hit: 9 for  14 radiant damage

Bonus Action: Archer strike To Hit: 23(17+6) for 4 radiant damage

Move: retreat 30 ft backwards towards Aranor

Starry Walt backs up, a flash of light streaking from his cosmic fingertips but missing the form altogether. Then he fires a luminous arrow which hits, although it does minor damage to the incorporeal form.

The entity floats forward, lunging for Zartan:
Attack: 18  Hit: 19 necrotic damage, and Zartan must succeed on a DC 14 Constitution saving throw...

Zartan and Aranor may act next!

As a reaction Zartan casts Silvery Barbs.

Silvery barb reroll: 
Biza Attack vs Zartan: 26.  Hit: (Same damage.)  Save: (Already made.)
Zartan shrugs off the strange coldness he felt from the Biza's grasping semi-corporeal hand.

The returning guard rushes forward and throws his spear at the smoky entity:
Spear Attack: 13. Hit: 2 piercing damage.

Kala continues to sleep.

Walt and Aranor may act next!

Walt, unfazed by his lack of success thus far, launches another attack from the Archer. He continues to retreat away from the threat and positions himself a step or two shy of the pier. Walt raises his hands to the heavens, shouts the incantation for call lightning and conjures a lightning storm above the ghostly apparition of Proud Edun.

Bonus Action: Archer strike to hit 19 for 7 lightning damage

Move: move backwards towards the pier. He will stop on square shy of standing directly on the pier.

Action: cast call lightning in a space above Proud Edun. I want to position it so that it will NOT hit Zartan. Dex save 14. On a failed save target takes 16 lightning damage. On successful save target takes 8 lightning damage.

Starry Walt backs up to the edge of the wooden pier and loosens another cosmic arrow. This one passes right through the unsettling entity, and definitely catches its attention. (That's radiant damage, correct?)

Calling the storm clouds into what was otherwise a clear day, Walt pulls down a bolt of pure energy from the heavens, making everyone left on the streets involuntarily shout and run. Biza DEX save: 5 

The bolt scores a direct hit on the floating form, and although it does not dodge it, it seems to do less damage than it might to a physical enemy. (Damage 8 with failed save.)

"You will regret helping these murderers and covenant-breakers," she shrieds. "Instead of giving up their firstborn children to serve as my apprentices in the forest, as they agreed in payment for my services, now they shall join me in death, as shall you."

(Whoops! Sorry, Zartan – you rolled your save and made your Reaction, but I forgot to give you your Action! You're up next!)

First Zartan thinks about what damage would be best for this type of creature and then blasts it.

Arcana: 8

('ll play out the next part, just unsure of the Damage type to use. If he got it, then the damage would be of that type. If he didn't then he would go with Lightning Damage)

Bonus Action: cast [Dragon's Breath] 

Action: Blast the breath at the creature so that it would not hit anyone else.

Damage is 12 (or half if it saves)

Zartan has never seen an entity like this before. 
Stepping to his left, he exhales a 15-foot cone of pure electricity. The Biza attempts to dodge it: DC15 Dex Save: 10

The incorporeal, smokelike skeletal figure reaches out toward the attacking guard, who is beginning to scramble around the cart to pick up his spear:
Touch Attack vs guard: 24. Hit: 21 necrotic damage and guard must succeed on a DC 14 Constitution saving throw: 6

The biza seems to almost absorb the lightning, its form barely reacting to Zartan's crackling breath.
The guard manages to dodge the biza's grasping, smoky hand. 

The guard steps over Kala's sleeping form, grabs his spear, and tries to plunge it into the unearthly monster.
Spear Attack: 18. Hit: 7 piercing damage

Everyone may act (including Zartan.) Storm clouds continue to swirl over the street. The biza is not unharmed, but it is far from defeated. And it is enraged.

Walt watches as Proud Edun diverts their attack to the guard and shouts ”Zartan! Get outta there!”

He runs towards Zartan and launches another volley of [Tooltip Not Found] followed by an Archer strike upon the ghostly apparition.

Move: 15 ft closer towards Zartan.

Action: cast [Tooltip Not Found] to hit 10 for 10 radiant damage. IF that attack hits, next attack against the target is with advantage.

Bonus Action: Archer strike to hit 9 ( or 22 with advantage from guided arrow. Damage: 8 radiant damage