Jurgen tears up the stairs and past the bugbear guard (#6) blocking the hall (but not quite out of its melee). He slashes into the first of the two (#1 and #5) grappling Ruven, burning green flames jumping from one to the next. They are both bloodied.

Meanwhile, Draco is successfully held at bay by the bugbear guard (#6).

Bryony and Ruven (grappled) may act next.

The two bugbears (#2 and #4) guarding Nezznar try to pummel Boona into submission:

#2 Morningstar Attack vs. Boona: 24. Hit: 6 piercing damage (non-lethal).
#4 Morningstar Attack vs. Boona: 7. Hit: 17 piercing damage (non-lethal).

Also coming to Nezznar's rescue is Bugbear #3, who leaps the stream, but finds that the massive glob of arcane webbing has created a bit a bottleneck. It decides to throw a javelin at Boona, instead:
#3 Javelin Attack vs. Boona: 10. Hit: 7 piercing damage (lethally intended).
Bryony may have an opportunity attack vs. #3 if she wishes.

#5 smashes Quinn:
#5 Morningstar Attack vs. Quinn: 21. Hit: 7 piercing damage.

#6 batters Draco:
#6 Morningstar Attack vs. Draco: 19. Hit: 8 piercing damage.

#1 lifts and carries a squirming Ruven toward the rift, past Bryony and Quinn.
(Bryony may choose to opportunity attack it as #1 passes. Only one opportunity attack per turn, of course; I believe Quinn has already used his on Vhalak.) 

Everyone may act!  

Boona ignores the ineffective bugbear attacks and brings down the maul once more on the drow.

Attack: 8 Damage: 14

Quinn is staggered by the strike from the bugbears massive morningstar. He's heavily bloodied and not looking good. He closes his eyes, time slows and images of bodies of Sir Roderick, Kimberly and Nundro flood his mind. He see's flashes of the elders and children from his village. He feels a surge of adrenalin, his eyes snap open and see's red. He spits a mouth full of blood in the face of the bugbear, marks it as his prey and rains down a heavy strike on the bugbear.

Bonus Action: Hunters mark on the bugbear in front of him.

Attack: 25 to hit for 18 damage (11 + 5 colossus slayer + 2 hunters mark)

Bryony lashes out at the bugbear carrying Ruven away as it passes her. Then she attacks again, attempting to sink her blades deep into its flesh. After that's done, she drops her dagger and pulls out the pouch of ball bearings she bought in Phandalin, scattering them all around her and the bugbear, hoping to make it trip and let go of Ruven.

AoO: 9 to hit, miss :(

Movement: Move up behind Bugbear #1

Main: Shortsword - 13 to hit for 9 damage (probably a miss though)

Dagger - 15 to hit for 5 damage

Bonus: Fast Hands - > Use an Item -> Drop ball bearings 10 feet around herself

Bryony tries to stop the bugbear carrying a squirming Ruven, chasing it toward the edge of the rift. Her blades have difficulty on its tough hide armor (AC16), but with its shield dangling low as it carries Ruven (-1 AC) she just manages to slip a dagger into its ribs. It bellows in pain but continues to stagger toward the precipice, not yet realizing that it is about to step into a sea of ball bearings.

Boona similarly struggles with Nezznar. Although he wears no visible armor, the slight shimmer she sees as the mace lands suggests he has a magical film of protection.

But Quinn, summoning every ounce of power he can, crushes the skull of his foe. It collapses heavily, quite dead. 

Nezznar, facing Boona, appears to be in a bit of a panic. "Get it away! Get it away!" he shrieks to his trio of goons. He disengages, then backs away down the corridor to the north, out of view. Vhalak likewise vanishes through the doors down the hall to the west.

Ruven and Jurgen may act!

Jurgen attacks the bugbear next to him, as does Draco.

10 to hit for 15 damage

Draco NAt 20 with 15 damage

Jurgen has trouble hitting bugbear #6, but Draco doesn't. Jurgen's steel mechanism tears a bloody chunk out of the distracted goon. 

It spins and retaliates:
Bugbear #6 Morningstar Attack vs. Draco: 10. Hit: 12 piercing damage.

Meanwhile, Bugbear #1, dancing warily away from Bryony (Disengaging from her), moves toward the ravine, still carrying Ruven. Distracted, it steps on the ball bearings. DC 10 Dexterity saving throw or fall Prone: 22 

The other three pile on Boona:
Bugbear #2 Morningstar Attack vs. Boona: 12. Hit: 12 piercing damage.
Bugbear #3 Morningstar Attack vs. Boona: 10. Hit: 8 piercing damage.
Bugbear #4 Morningstar Attack vs. Boona: 23. Hit: 8 piercing damage.

Somehow, Bugbear #1 remains on its feet, still holding Ruven, but somewhat unnerved. Then it unhesitatingly tosses Ruven into the pit. (Ruven takes 7 bludgeoning damage unless he has any tricks up his sleeve!)

Vhalak and Nezznar are nowhere to be found.

Everyone may act!

Quinn glares at the bugbear as it tosses Ruven down into the pit. He marks that bugbear as his prey, clips Lightbringer to his belt, draws a dart and launches it at bugbear #1.

Bonus Action: Transfer Hunter's Mark to bugbear #1

Attack: 21 to hit for 16 damage (5 + 6 from colossus feat + 5 hunters mark)

(OOC: bugbear is vexed: Quinn has adv on next attack)

Boona broke away from the bugbears ( all get AoO) and loped after the drow.

Dash ( 70ft move)

Or if he is close enough to catch with 35ft movement she will hit him- Attack: 25 Damage: 16

Bryony lets out a sound of frustration as her ball bearings fail to bring the bugbear down. He is able to throw Ruven over the cliff, and Bryony rushes to catch up and sink her blades into the bugbear's back as revenge.

Shortsword - 24 to hit for 10 piercing damage

Dagger - 11 to hit, assuming a miss (even with Vex, I still got such a low roll lol)

Boona turns and chases the drow. The three bugbears do not hesitate to try and stop her:
 Morningstar Attack vs. Boona: 8. Hit: 14 piercing damage.
 Morningstar Attack vs. Boona: 6. Hit: 11 piercing damage.
 Morningstar Attack vs. Boona: 22. Hit: 9 piercing damage.

But she tears away from them. Boona indeed catches up with Nezznar as he is climbing a set of stairs, but he successfully dodges her mace.

Quinn throws a dart at Ruven's recent captor, hitting it square in the eye as it turns. It screams, staggers back a step, slips on a ball, and plummets backward off the ledge.

Bryony begins to race forward but sees her mark fall off the cliff. (Would she like to redirect her attack to the bugbear just across the stream? She can just make it to him with her movement.)

Jurgen and Ruven may act!

Bryony watches with amusement as the bugbear trips on a ball bearing and falls off the cliff. With that one taken care of, she instead heads for the next nearest bugbear and delivers her attack against that one instead. 

Bryony jumps and splashes across the noisy cave stream and sinks her shortsword into bugbear #3's back. It shouts and spins to confront the halfling.

Jurgen and Ruven may act!

Nezznar points his spider-tipped staff at Boona.
"Get back, you freakish oaf!" 
Three glowing arcane darts fly out of its leggy tip directly into Boona's chest. Boona takes 10 force damage.

Boona finds herself flanked by two bugbears behind her, who continue to try to pummel her with their morningstars. 
Bugbear #2 Morningstar Attack vs. Boona: 7. Hit: 12 piercing damage.
Bugbear #4 Morningstar Attack vs. Boona: 10. Hit: 10 piercing damage.

Meanwhile, Bugbear #3 turns its attention on Bryony:
Bugbear #3 Morningstar Attack vs. Bryony: 6. Hit: 7 piercing damage.

and Bugbear #6 bashes Draco:
Bugbear #6 Morningstar Attack vs. Draco: 21. Hit: 10 piercing damage.

Everyone may act!

Boona looked back over her shoulder at the two bugbears with an annoyed sideye then swung at the drow again.....the magic bolts had hurt a lot and she was beginning to feel a bit sleepy for some reason but she didn't dwell on it.

Reaction- Stones Endurance- 13

Attack: 24 Damage: 12

Boona's maul glances off the sparkling arcane protective barrier surrounding the badly wounded Nezznar.

The rest of you have lost sight of Boona but can hear her cries as she is shot with arcane missiles even as she holds off a flurry of heavy Morningstar swings.

Bryony (facing an angry bugbear goon), Jurgen (likewise), Ruven (bleeding at the bottom of the ravine, and possibly unconscious), and Quinn (alone on the stairs near a felled bugbear) may act! 

Quinn runs around the corner towards Bryony. He spots the bugbear tangled up with Bryony, marks it as his prey and crashes down upon it with Lightbringer.

Move: full movement speed to engage the bugbear

Attack: 21 to hit for 18 damage (9+ 4 hunters mark + 5 colossus slayer)

(OOC: If the bugbear is NOT at max damage, total damage dealt will be 14)

Quinn yells out to Ruven.

"Ruven! Where are you? Do you need help?"