Phandelver and Below: The Shattered Obelisk

Jurgin shakes off the sleep and steps in to attack. He moves to a good vantage point and casts Burning Hands again. He then has Hero move forward and attack the nearest one. 

Action: Cast Burning Hands 8 points of Fire damage or Save DEX 16 for helf

BA: Hero attack 15 to hit with 5 Force Damage

(Silvery-barbed reroll: Wight Necrotic Bow Attack #2 vs. Jorzu: 15. Hit: 5 Piercing damage plus 7 Necrotic damage.)

(Jurgen may only make a DC10 WIS Save to try to shake off the sleep this turn. If he fails again, he goes fully unconscious. Hero can only Dodge for now.)

Jorzu (if available) and Bryony may act.  Boona and Bryony should also save vs. dust damage.

Boona Disadvantage Wis Save-   -  13 or 5

Follow up

Boona Wis Save-  11

Bryony, Karst, and Hero try to mitigate the spray of dust from the exploding mephit:
Bryony DC10 Dex Save: 8
Karst: DC10 Dex Save: 5
Hero: DC10 Dex Save: 8
(Take 5 Bludgeoning damage on a fail, or 2 on a success. Boona manages to partially dodge it, taking only 2 damage.)

The three surviving dust mephits laugh with amusement, seeing Boona and Jurgen fall prone, seeing their wight assistant felled, seeing their three comrades obliterated. They laugh and laugh.

Fergus (still concentrating on Confusion?) Jorzu (if available) and Bryony may act next.

Fergus:

Maintaining concentration on the spell that appears to be keeping the dust mephits occupied, Fergus aims a pair of Radiant Notes at the one farthest away, hoping that if it bursts it will injure its fellows instead of his allies.

Radiant Notes (Starry Wisp):  Attack: 27 Damage: 15

Bryony managed to shrug off the worst of the dust mephits' attack. She engages with the nearest one and attacks it with her blades. Once she's done that, she'll try to move out of melee range of the mephits.

Action: Shortsword - 13 to hit for 6 piercing damage (if it's a hit, I'll roll advantage for Vex); Dagger - 26 to hit for 6 piercing damage (Nick) + 15 sneak attack damage if it applies (ally in melee OR if Vex gives advantage)

BA: Cunning Action - Disengage

Bryony manages to get two blades into mephit #3 before dancing away. Like the others, it explodes into a spray of debris, mostly hitting Quinn. Quinn: Make a DC10 Dex Save, taking 7 Bludgeoning damage on a fail, or half damage on a Success.

Their laughing paused for a moment, the two surviving mephits begin calling out in a strange language. (Does anyone speak Primordial – Auran or Terran?)

Then they again try to let their dust lull you back to sleep. Boona, Karst, Quinn, Bryony, and Jurgen: Make a DC10 WIS Save, or collapse, incapacitated, as you fall back asleep... Quinn, caught between two such effects, must do so twice.

Fergus "aims" his discordant chords at mephit #6, which survives (barely) the concussive impact of the notes, but struggles to maintain its sleep spell (DC10 CON Save vs. Concentration: 15)

(Fergus interrupts the second sleep spell - Bryony and Jurgen are spared its effects, and Quinn may only roll once.)

Two squalling dust mephits remain. Boona, Jorzu, Bryony, Quinn, and Jurgen may act. (Boona and Jurgen - do you want me to parse your last turns, or do you wish to take a difference course of action?)

DEX save: 11 (5 + 6)

WIS save: 11(9 + 2)

Quinn raises his shield just in time to take the brunt of the explosion. Quinn darts in to attack the two remaining dust mephits.

Move: Use full movement speed to get into melee range. If Quinn takes the first one out, he'll use any remaining movement speed to engage the other target.

Attack 1: 23 to hit for 10 damage (savage attacker feat to reroll my damage)

Attack 2: 26 for 11 damage

Jurgin stands up, shakes off the sleep, and steps to the front line to attack. He moves to a good vantage point and casts Burning Hands again. Burning Hands: 8 points of Fire damage or save DEX 16 for half damage. The two surviving dust mephits try to dodge the thin, but spreading, sheet of flames: DC16 Dex saves: 13 and 22 . 

Hero moves forward through the group and attacks the nearest (#4).  Hero: attack 15 to hit for 5 Force Damage. 

The levitating creature in the rear detonates in a spray of dust, which its comrade tries to dodge. DC10 Dex Save: 20

Clearly injured, the last dust mephit continues to shout and gesticulate in an unearthly tongue, pointing with frustration at the closed door to the west.

Then Quinn steps in, and with two swings of his radiant mace, releases this final mephit from the Material Plane. It explodes. 

Hero, Jurgen, and Quinn: Make a DC10 Dex Save, taking 5 Bludgeoning damage on a fail, or half damage on a Success.

Combat is over. Everyone may act. The mephits are gone, a mess of dust and debris left behind, together with the dessicated corpse of the dispatched wight.

Fergus:

Releasing his concentration on the spell, Fergus moves up and asks, “Is everyone okay? Could anyone understand what they were saying?”

Boona shakes her head, " Not realise I am so sleepy......sorry, napping in fight very unprofessional."

She moves towards the door to her south-west but just sits down in front of it.

Boona takes a short breather near the substantially-fortified door, which she notes is heavily battered from this side, and absolutely covered in fine dust. It has three keyholes, choked with dust.

Dex Save: 12

Quinn shakes his head like a wet dog trying to rid himself of all the dust mephit debris. He walks over the wight and sifts through their remains to see if they have anything of note 

"It's okay, Boona," Bryony says, joining the giant at the door. "They made me very sleepy too."

Bryony examines the door and is surprised to see the three keyholes. "I guess they wanted to make sure whatever is behind this door is locked up extra tight," she says, thinking out loud.

Quinn is disappointed to find that the wight is carrying absolutely nothing. Even its sword and bow seem to have decayed into worthless scrap since the wight was dispatched. 

All is quiet. 

Quinn walks over to the western door. He stands in front of it and ponders the damage to the door. He delicately pokes at the debris plugging up the holes. He attempts to commit the shape of the keys to memory.

"Whoever locked this door, really didn't want anyone to get in there."

Quinn raises a finger to his mouth asking everyone quiet for a minute.

He places his ear against the door listening for a bit. He knocks on the door and then listens. He then pounds on the door with Lightbringer and again listens for anything on the other side.

Perception check: 20

DM: About the damage on the door, does the damage appear to be made from weapons, claws, magical damage, etc? 

The door has been battered by claws, swordmarks, blunt objects, various tools, you name it... Quinn determines that one of the three locks has been sprung. The other two - relatively substantial locks of Dwarven manufacture - are caked with dust and obviously-failed attempts at picking them. Listening at the door – before and after banging on it – he hears absolute silence.