Endelyn hisses at Ben, as her little extra arms flash the puppeteer's lash once again:

Endelyn: Puppeteer's Lash vs. Ben: 7 Hit: 13 psychic damage, and Endelyn tries to telekinetically throw him over the railing into the crackling electrical field.
Then she moves on the double doors at the west end of the ring balcony, opens them, and enters. (Ben may have an opportunity attack if he's still around.)

The remaining darklings again catch up with Glister in the Orrery. Four of them again try to grapple her:
Darkling #7: STR check: 18 Glister's contesting acrobatics check: 10
Darkling #8: STR check: 17 Glister's contesting acrobatics check: 22
Darkling #10: STR check: 5 Glister's contesting acrobatics check: 15
Darkling #11: STR check: 19 Glister's contesting acrobatics check: 16

Ben goes flying. (Make a DC15 Acrobatics check to grab the railing and avoid a dangerous fall, else: take 6 bludgeoning damage and then make a new DC 15 Dexterity saving throw at disadvantage (due to metal armor), taking 55 lightning damage on a failed save, or half as much damage on a successful one.)

Despite her gymnastics, Glister is grappled by two of the darlings.  Titaani catches up with the others, and is at the bottom of the central stairs.

Everyone may act!

Horatio barrels ahead towards the sound of fighting. 

Matilda moves quickly but is stymied by the closed doors.

( NA )

Endelyn finds that Ben is partially protected from her Puppeteer's Lash...
Endelyn (disadvantage roll): Puppeteer's Lash vs. Ben: 11  If hit: same consequences as above.

Horatio's dash up the stairs brings him as far as the broken-mirrored balcony.

Matilda races after Endelyn, but finds that the double doors have shut behind her. (She may still have her action and bonus action.)

Titaani, Ben, and Pud may act, and Matilda (who moved 30') may still have her action.

Ben:

Seeing his death flash before his eyes but be averted due to his divine protections, Ben shoves Creeping Lyn as she tries to push past him and head towards the double doors.

Opportunity attack to Shove the hag over the rail and into death by electrocution:  Athletics:  17

(Regular turn to follow later).

(Edited to hopefully force roll)

Before Endelyn can disappear through the double doors, Ben tries to turn the tables on the hag, defying her telekinetics and giving her an old-fashioned shove.

Endelyn DC12 Contested Strength check: 9 

Endelyn: DC15 Acrobatics check to grab the railing and avoid the fall: 10

...If she fails, she takes 5 bludgeoning damage and then makes a new DC 15 Dexterity saving throw, taking 45 lightning damage on a failed save, or half as much damage on a successful one: Dex Save: 6

Over she goes, her hands not quite catching the railing. BLAM! She is immediately struck by lightning before she even hits the ground.

Endelyn disappears in a cloud of inky smoke. There is no impact.

Titaani, Ben, and Pud and Matilda may act. (We can retcon Matilda's move.)

Ben:

Standing for a moment in shocked silence that his maneuver had actually worked, Ben gives a silent prayer of thanks to Sune.  Seeing the Darklings swarming Glister below, he springs into action, using Misty Step (from his Fey-Touched Feat) to bring him directly next to them below (plus any moving as needed).

"Creeping Lyn goes down to defeat.  Now each of you return to your seat!" he instructs the hostile Darklings, using his holy symbol of Sune to add weight to his command.

(Channel Divinity:  Turn the Faithless - As an action, you present your holy symbol, and each fey or fiend within 30 ft. of you that can hear you must make a WIS saving throw (DC 14). On failure, the creature is turned for 1 minute or until it takes damage).

Matilda was utterly shocked to still be alive but then she looked around desperately for Titaani, " SIS! You still alive?"

Pud continues running as fast as he can. His wonky leg is getting sore, but he pushes through and does his best to keep up with the group. He'll dash to cover as much ground as possible.

Titaani hears Matilda calling for her and frantically looks around for her. "I'm alive! Are you ok, sis? Where are you?"

Investigation (to find Matilda): 20

If Titaani is able to find out where Matilda is, she'll use all of her movement to get there. 

Pud and Titaani race up the stairs, making it as far as the landing.

Ben vanishes in a cloud of silvery mist, reappearing next to Glister and her captors. They stare wide-eyed at Ben before some of them scatter.
Darkling #7 (holding Glister): DC14 WIS save: 12
Darkling #10 (holding Glister): : DC14 WIS save: 18
Darkling #8 (tried to grapple Glister): : DC14 WIS save: 21
Darkling #11(tried to grapple Glister): : DC14 WIS save: 18
Darkling #5: DC14 WIS save: 8
Darkling #9: DC14 WIS save: 2

Glister is freed. Her two captors and two other darklings race back out the way they came, terrified, getting as far as the broken mirror. The first pushes through, coming face-to-face with Horatio. Only two darklings remain by Glister and Ben, unsure what to do next. Then they back away slowly (disengage) and bolt after their companions.

Glister growls, but doesn't chase them. Instead, she looks warily around for Endelyn, who remains vanished. The machine continues to crackle and whir, scattering small puffs of smoke. 

Elkhorn, and Amidor chase after Titaani.
"Wait up!" shouts Squirt, hovering quickly over.

Everyone may act!

Seeing two more enemies bearing down on him, Horatio gives the oncoming Darklings no quarter. 

(( Unarmed Attack 1: 10 to hit, 15 to damage - includes 3 from Giant's Might d6 ))
(( Unarmed Attack 2: 14 to hit, 13 to damage ))
(( Bonus Attack: Nat 20, 17 to damage ))

He will stay and engage if they survive, but if they are dispatched he will continue up the stairs to find the others. If they try to move past him he will warn the others below. 

Ben:

“Glister, where is your sister?  The hag was headed towards the double doors upstairs when I bumped her into the lightning—maybe we’ll get answers there…” he says, moving back to the spiral stairs and up, planning to get back to his previous position and continue on to the unexplored doors.

(Move and Dash)

Not listening to Squirt, Titaani continues to race towards Matilda's voice. (Movement and dash) 

Unsure, Matilda made her way slowly towards the stairs leading down...