Quinn yells out to Bryony and Ruven.

"Bryony...Ruven! The dwarf is escaping. Flank to the double doors to the south."

Everything happens at once.

Boona surges ahead and slams Nundro, who races away in a panic. Boona swings and misses.

Boona follows, taking the brunt of a pair of parting swings by the bugbears. Opportunity attacks:
 #2 Morningstar Attack vs. Boona: 7. Hit: 4 piercing damage.
 #4 Morningstar Attack vs. Boona: 20. Hit: 9 piercing damage.

Quinn mystically marks the fleeing dwarf, then shifts his attention to the wounded and distracted bugbear, felling it. As to the dwarf, he senses no Immunities, Resistances, or Vulnerabilities, other than an Immunity to being Charmed.

Bryony helps Ruven up the rope and out of the rift (assuming that is what he wants to do.)

(How's Boona doing?)  (BTW: Draco was blocked from attacking by the front line fighters.)

Nundro vanishes around the corner and races up a flight of steep stairs (followed by Boona if she's up.)
The remaining bugbear disengages and follows.

Everyone may act.

( Boona has 6 hp.)

Jurgen casts Cure wounds on Boona for 17 HP

BA - Jurgen lets out a cry at enemies within 10 ft. of you. Until the start of my next turn, you and your allies have advantage on attack rolls against the enemies that could hear you.

Bryony hears Quinn's call and after giving Ruven a quick check to make sure he's mostly intact, she races back toward the main group. She just makes it in time to see the dwarf who may or may not be Nundro racing up a flight of stairs.

"Stop running!" she shouts and brings out her shortbow. If she has line of sight, she'll release an arrow intended to slow the dwarf down.

Action: Shoot "Nundro" with an arrow if he's within LOS, 24 to hit for 9 damage

Bonus Action: Cunning Action to Dash 50 ft

Quinn rushes in at the last remaining bugbear, spurred on by Jurgen's war cry and attacks with Lightbringer.

Attack: 17 (w/ADV) to hit for 13 damage (or 10 damage total IF the bugbear was at max HP).

IF the bugbear goes down, Quinn will use his remaining movement to pursue the dwarf. Otherwise he stands pat wanting to avoid an AoO.

(OOC: I used my Savage Attacker feat to roll damage twice and chose the higher number.)

Boona races after Nundro but can only watch as he ducks into a room and south around a corner. The remaining bugbear is appears behind him on the stairs, just out of melee range. (Boona may still move and act this turn, as her initial whack-and-chase was last turn.)

Bryony dashes, but can only get as far as Quinn and Jurgen. (I'm assuming she'll use that attack roll against the bugbear instead?) She hits the (previously uninjured) bugbear with her arrow.

Quinn whacks the arrow-stuck bugbear and nearly takes it down, but it is still up and alive (and rather panicked.)

Boona is up next!

Boona runs into the room and turns south seeking Nundro.

If he's in sight she will attempt to hit him- Attack: 25 Damage: 12

If he's not in sight she will start smashing the southern wall with her maul in suspicion he somehow went through it.

Boona finds herself in an ancient temple hall. Cracked and splintered marble pillars line its walls. A nine-foot-tall statue of a dwarf seated on a throne, a mighty stone warhammer across his lap, occupies the north end. Large emeralds gleam in his eyes. Dust and debris have been swept to one side of the floor. Half a dozen bedrolls and packs are neatly arranged around a rough-built firepit before the statue. A wooden table stands on the west side of the room between two pillars.

 But the temple is otherwise empty of inhabitants. No sign of Nundro.

The remaining bugbear, badly bloodied, turns and thrashes out at Quinn in a panic before making a break for the temple to the west (without disengaging; Quinn may have an opportunity attack.)

Morningstar Attack vs. Quinn: 22. Hit: 15 piercing damage.

Everyone may act!

Jurgen and Draco will move forward towards Boona.

If he has sights on the Bugebear at the end of the hallway he will fire his crossbow (21 to hit with 7 damage).

Draco he will direct to dash to Bonna's side and provide his deflect attack Reaction for her

Steel feet clatter on stone as the mechanical beast gallops both sets of stairs. But by the time it reaches Boona, Jurgen's well-aimed arrow has taken down the last bugbear.

Nundro is gone; all other enemies are slain. Everyone may act.

Quinn runs to the side of Boona and searches for blood trails or signs of Nundro.

Survival check: 21 (w/ADV due to Hunter's Mark)

The doors to the south are slightly ajar, Quinn notices, and a smear of blood is visible on the handle.

Boona watches Quinn inquisitively, if he gives the nod she will barge through the doors then Dash left looking for the weird dwarf.

Boona finds herself back in the hallway they just left. No sign of Nundro.

Jurgen will dash as will Draco to be next to Boona

Boona looks confused.....did the dwarf run in a circle or run south....how can tiny legs be so fast?

She ran south to the intersection of the water on her right and destroyed undead on her left then huffed loudly and punched the wall in frustration.

Jurgen races ahead, catching up with Quinn. Draco clatters forward, pausing at the top of the two staircases in the hall.

Boona runs to the entrances of W10 and W11. There is no sign of Nundro. The waters of the pool remain still, and the dead bugbears piled to the east remain at rest.

Bryony does her best to catch up with Boona. She sees the giant's frustration as she punches a wall. Nundro is nowhere to be found. 

"Let me see if I can pick up his tracks," she tells Boona.

Bryony then scans the area looking for any signs of Nundro, perhaps a blood trail or footprints that belong to a dwarf.

Survival - 21