Perhaps overconfident, or just lazy, all of their attacks fail to hit their mark.

Garrin moves up to the corner (two squares north) and waves his staff in a swirling gesture. "Ka-la!" He shouts the magic word as glowing moths appear in a clinging cloud around the bugbears

Casting faerie fire DC 13 dex save

Droknin will just let the prey gloat, and he will strike at the injured one.

Mlinzi Attack1: 16 Damage: 6

Mlinzi Attack2 (BA): 9 Damage: 7

Held Attack Action: Attack: 20 Damage: 4

Keashirryl moves as close as needed to have line of sight on the bugbears, pushing against the wall to get out of the way, while attempting sacred flame  one more time (DC 12 dex save) . She keeps a close eye on the state of both Cassius and Droknin, seeing the sheer force of the bugbears' missing blows. 

T'laren waits for a way forward to clear, but it doesn't happen - his allies remain single file in the hall.  

Garrin unleashes his glowing butterflies on the bugbears.  One fails to shake them off and is illuminated in shimmering light.  [Advantage on attacks against the outlined bugbear.]

Cassius hangs back with an attack readied, but the bugbears remain out in the chasm chamber fighting with Droknin.

Droknin continues to hold the line, surrounded by bugbears.  He manages to cut down the one that had been previously wounded by T'laren's arrows and he deals a superficial wound to the glowing bugbear.

Keashirryl summons a spot of holy flame to fall upon the javelin wielding bugbear on the bridge, but he swats it away without effect.

T'laren hears the secret door behind them open again and Sildar Hallwinter emerges.  "On second thought, I thought you folk might need a hand down here.  It sounds like you're already in a fight.  What is happening?"  He draws his longsword and moves down the hall toward T'laren.

1. Sildar Hallwinter
2. T'laren
3. Cassius
4. Bugbears
5. Garrin
6. Keashirryl
7. Droknin

T'laren looks back at Sildar. They'd left him wounded from his fight with the "Townmaster", but if that version had been the wizard himself, he'd know what wounds he'd given to the real Sildar... and he'd know the names of the party, having been there during their first visit.

The wood elf sighs. With no good way to confirm that this is or isn't the real Sildar... "If it's really you, I'm sorry."

Longbow Attack: 24 Damage: 5

((He was apparently shooting to injure, not kill, until he knows if it's the real deal.))

Cassius will move to stand in the space of the now dead bugbear, readying his staff and unleashing a strike towards the hairy goblinoid to the right. Once that is done he follows up with a snap kick towards it stomach.

Attack: 16 Damage: 5

Attack: 16 Damage: 4

Quote from DarthDrizzt >>

Cassius will move to stand in the space of the now dead bugbear, readying his staff and unleashing a strike towards the hairy goblinoid to the right. Once that is done he follows up with a snap kick towards it stomach.

Attack: 8 Damage: 10

Attack: 6 Damage: 6

 At advantage due to Faerie fire?

[Rerolling to give advantage for Cassius on his two attacks... 24,  17 ]

T'laren looses an arrow at 'Sildar.'  It passes through the meat of his upper arm, spraying blood but not dealing much damage.  His eyes widen in pain, surprise... and then fury.  "What?  How... Grrrrrrrr... very well.  Thanks for the healing potion, fools.  And thanks for returning the townmaster to me.  Once I'm done with you, I can impersonate him or Sildar, as the need arises.  I won't even need these Redbrands and their wizard friends any more."  As it speaks, the voice changes slightly.  No longer the voice of the old human warrior, it is raspy and alien, the voice of a monster.

Cassius deals additional blows to the wounded and glowing Bugbear.  It is clearly hurt, but so far the wounds seem only to enrage it further.  "Gaaah!  I smash you!" it cries out.  The wounded bugbear continues swinging at Droknin with its morningstar, while the bugbear on the bridge uses its last javelin like a spear, stabbing at Cassius.

Attack on Droknin:  Attack: 24 Damage: 24

Attack on Cassius:  Attack: 5 Damage: 7

Both Bugbears connect, and the glowing Bugbear's anger fuels a powerful strike to the leonin barbarian.  Droknin is clobbered across the head and falls to the ground.  [Droknin, start making death saves this turn unless someone can heal/stabilize you.]

Droknin Death Save: 18

((Is it Garrin and Keashirryl up?))

[Yup.]

Garrin turns towards "Sildar" and waves his staff. "You'll be eating my staff, you reprobate!" Garrin tries to hit him with an eldritch blast

Attack: 18 Damage: Unable to parse dice roll. 

Keashirryl flinches, seeing Droknin fall, and the javelin that simultaneously sinks into Cassius. After a brief moment of panic, she grabs her holy symbol, and murmurs something that sounds too aggressive for a prayer, but too long for a swear word.

With that, she uses her action to channel divinity, dividing 10 HP between the two melee fighters (if Cassius is still at 6, then she gives 8 to Droknin and 2 to Kemp, otherwise divides equally).

Droknin, that healing would occur prior to your own turn.  You can pop back up and take a normal round instead of your death save.