Matilda begins throwing, kicking and pushing things off the balcony starting with the ornithopter.

Ben successfully fishes out the bench from the dangerous lightning zone, and hurls it one last time. Again it's ineffective, and the bench is now deep in the powerful electric field. Giving up, Ben begins to circumnavigate the chamber.

Meanwhile, Horatio flattens a fleeing Stagefright with a massive fist. Stagefright is now unconscious on the loading dock, never having quite reached the rope he was sprinting for. The two goblins on the cranes just gawk. 

Matilda kicks the ornithopter off the high balcony. (Free object interaction.) It doesn't seem to take any damage in the fall, but it nearly crushes a darkling in the stands.

Seven darklings race up the stairs after Ben, ignoring Glister. One manages to get through the mirror and into the Orrery, another as far as the balcony where Ben had been.

One darkling in the amphitheater tries to grapple Elkhorn:
Grapple attack: 2.  Elkhorn contesting Strength roll: 16

Three of them swarm onto the stage. One tries to grapple Pud:
Grapple attack: 11. (Pud must make contesting Athletics or Acrobatics check.)

Two try to grapple Titaani:
Grapple attack: 5.
Grapple attack: 10. (Titaani must make contesting Athletics or Acrobatics check for each.)

Ben sees movement above – Endelyn is crossing the Viewing Gallery, in the same direction as Ben. They are exactly opposite one another, across the orrery, on two different levels (she is 20' above and about 50' away.) Ben and Endelyn lock eyes for a moment across the moving, electrified machinery. You each have three-quarters cover from one another. 

Titaani and Matilda may act next. (And Pud must make a contesting check first, and Titaani must make two, first.)

Acrobatics check 1: 15

Acrobatics check 2: 4

I'll spend a luck point to reroll the second one: 21

Everyone may act, in any order.

Horatio takes the scepter from Stagefright, and anything else of note or possible value (( Investigation 18 )). He then throws the unconscious Stagefright off the edge towards the abyss. Then runs back to the stage area to find out where everyone else is (( Perception 14 )). 

Pud wriggles and squirms as he tries to break free of the unseen threat. He calls out for Rizzo for help.

"Rizzo! Help me! Blast 'em!"

Acrobatics check: 3 (nat 1 + 2)

Bonus Action: Force blast from Rizzo. To hit: 17 for 5 force damage.

IF Pud avoids the grapple, he will use his movement speed to blindly stagger away in a random direction. 

(OOC: I rolled a d12 with each number corresponding to the cardinal directions. I.E. 12 = North, 3 = West, etc.  I rolled an 8, so Pud would wander 30 ft NE.)

Matilda slips into the shadows and through the door after Lyn.....

Stealth- 20

As the two goblin crane-workers watch with astonishment and alarm, Horatio relieves Stagefright of his clowinish fool's scepter (which is topped with a visage similar to Stagefright's) before throwing him over the edge of the dock. Horatio doesn't hear Stagefright's body hit the bottom – it's a long, long, long way down. Stagefright had no other possessions of value.

Horatio then makes his way back to the amphitheater floor. He can see the commotion on and near the stage, but he doesn't know where Ben or Matilda went.

Still blinded, Pud wriggles out of the grasp of the darkling, as Rizzo blasts it with force, seriously wounding it. He staggers off the side of the stage, but not before the wounded one tries to stick him with his little knife. He staggers off near the back of the stands.
Dagger Attack vs. Pud: 17 Hit: 6 piercing damage plus 12 necrotic damage.
(Pud still has an action if he wants it.)

Matilda opens the door and creeps through the hallway after her. In front of her, she sees a ring-shaped balcony. The stone railing that encloses it has balusters shaped like hourglasses. Beyond the railing she can see a massive copper pole made of ten-foot lightning rods attached end to end. It extends upward through a hole in the domed ceiling. Endelyn is walking briskly around it, toward the west, although she pauses for a moment as she sees something below her. Matilda can yet see what lay below. 

Titaani and Ben may act next.

Ben:

”Sun, Moon, and Stars—they’ll leave you with scars!” calls out Ben as he focuses on the Hag, bringing down holy flame on her as he keeps moving towards the staircase!

Sacred Flame, DC 14 Dexterity to avoid, ignores cover:  2

Then moving 30 feet onto the staircase (headed up).

Ben makes his way nearly to the other side of the electrified chamber as he evokes a flame-like radiance upon the hag above. (DC 14 Dex save: 2 )

Matilda hears Ben's rhyme from below as she creeps ever forward, within ten feet of Endelyn. (Expeditious Retreat - sorry, forgot!) Still clinging to the shadows, she can now catch a glimpse of Ben, below.

Glister pushes past the darklings and climbs through the hole in the mirror after Ben.

Amidor and Elkhorn both engage the darklings in swordplay as Pollenella buzzes blindly and angrily overhead.

Amidor vs. Darkling #5: Rapier Attack: 18. Hit: 9 piercing damage.

Elkhorn vs. Darkling #4: 
Longsword Attack #1: 20. Hit: 4 slashing damage.
Longsword Attack #2: 10. Hit: 4 slashing damage.

Titaani is up next!

(( Does Horatio see Titaani surrounded on stage? ))

( Hmmmm, any chance she's distracted enough by whats below that an attack would qualify for Sneak Attack?)

As Pud staggers away he blindly attacks in the general direction of whatever tried to grapple him.

(OOC: DM see Discord for my thoughts on Pud's attack.)

Attack with Acid Splash:  Targets make Dex save 15 or take 11 Acid Damage

OR...

Attack with Fire bolt. To hit: 16 (w/disadvantage) for 8 fire damage. 

(( Does Horatio see Titaani surrounded on stage? ))

Yes, he does.

( Hmmmm, any chance she's distracted enough by whats below that an attack would qualify for Sneak Attack?)

Matilda is currently unseen, so if she were to do a ranged attack at the top of her next turn, it would be at advantage, and that would qualify her for a sneak attack.
But if she were to attempt a melee attack, though, I'd ask for another stealth check first to see if she can mask her approach.

(Does that rules interpretation seem sound?)

Pud blindly hurls a mote of liquid fire in the direction of the darkling that tried to knife him. He hits it. It, too, immolates in a blinding flash.

Amidor and Titaani must make a DC 10 Constitution saving throw or be blinded until the end of their next turn, as do the two other darklings.
DC10 CON saves:
Amidor: 7
Darkling 3: 21
Darkling 5: 9
Titaani: roll a DC10 CON Save

Pud's vision, however, comes back.

Titaani may act next (and do so just before the blinding flash.)

Quote from cbaer8 >>

(Does that rules interpretation seem sound?)

 ( Yep. Nice.)

Seven darklings begin to swarm through the broken mirror and into the Orrery after Ben, ignoring Glister. One gets within 10 feet of Ben; he can see three others in the chamber with him.

One wounded darkling tries to knife Elkhorn:
Darkling #4 vs Elkhorn: Dagger Attack: 18. Hit: 7 piercing damage plus 4 necrotic damage.

Two darklings try to grapple Titaani:
Darkling #5 Contested Strength check vs. Titaani: 4
Darkling #3 Contested Strength check vs. Titaani  14

Titaani should make two contesting Athletics or Acrobatics checks against the grapples, as well as a DC10 CON save to avoid being temporarily blinded by the flash.

Everyone may act!