Kasbis would not be using a torch, would be relying on his dark vision when he is watching, on lookout.  

Hrathen does get out a torch so he can see, and points out the motion to the group.

As the cleric pulls out a torch to light it Duncan quietly snaps at him, "Do you want to just send up a damn flare announcing our location to everyone with a mile?!" 

You see 3 of these creatures rising from the sand. Roll initiative and post your actions.

Dust Mephit 1 initiative 19

It attacks Duncan with its claw

Attack: 20 Damage: 5

Dust Mephit 2 initiative 12

It attacks Kasbis with its claws

Attack: 10 Damage: 3

Dust Mephit 3 initiative 10

It attacks Hrathen with its claws

Attack: 22 Damage: 5

Duncan Initiative 9

As the first dust creature appears and moves towards them, Duncan immediately responds with a quick attack. It then lashes out at Duncan, its claws digging into his side sharpening his focus. He returns the attacks by quickly bringing his glaive around again.

reaction (pole arm master opportunity attack when something enters my attack range): Attack: 17 Damage: 10
action: Attack: 17 Damage: 6
bonus action: Attack: 21 Damage: 5

Kasbis initiative : 10 

Gaz remains curled up inside one of his inner pockets.  

When the dust creatures appear, Kasbis pulls a little bit of sand / mica out of his pocket and tosses it in the air, shouting “Calambusto!”  He casts shatter at a point behind the dust mephits, to encompass them but not affect Duncan, Hrathen or himself.  A sudden, loud ringing noise and a thunderous sound erupts.  The mephits take 13 thunder damage.  

(No disadvantage as they are made of sand and dust)

Dust Mephit 1

Con Save 5

Dust Mephit 2

Con Save 13

Dust Mephit 3

Con Save 11

(All the mephits pass and they move for the attacks as listed above)

Duncsan kills Mephit 1 and it explodes

Death Burst. When the mephit dies, it explodes in a burst of dust. Each creature within 5 feet of it must then succeed on a DC 10 Constitution saving throw or be blinded for 1 minute. A blinded creature can repeat the saving throw on each of its turns, ending the effect on itself on a success.

Hrathen initiative: 11

Hrathen looks at the mephits, then casts toll the dead on one of them. It is a dc 13 wis save or 9 necrotic damage.

Dust Mephit 3 Wis Save

16

The Mephit is unharmed by Hrathen's cantrip

Round 2 Post when able

Initiative Order

1. Kasbis
2. Dead Mephit 1
3. Duncan
4. Hrathen
5. Mephit 2
6. Mephit 3

Duncan, holding his breath as the dust of the first creature coats him, quickly turns his weapon towards the second.

action: Attack: 25 Damage: 14
bonus: Attack: 14 Damage: 7
((Note, if the other Mephits are in melee with his friends, Duncan will stay at range (he can attack from 10ft), to avoid future dust bursts))

Kasbis is startled when the dust mephits survive his attack and one has the audacity to attack him.  As a bonus action, he casts misty step to get some distance from the mephits, teleports 30 feet away from them.  Then he points at the closest mephit and force energy shoots out of his arm toward the mephit.  

Eldritch blast : Attack: 10 Damage: 7 force damage plus 2 points thunder damage.

Hrathen frowns at the failure to damage the mephits, and casts toll the dead on one of them again. It is a dc 13 wis save or 6 necrotic damage.

Mephit 2 and 3 die in an explosion

End of Combat

Death Burst. When the mephit dies, it explodes in a burst of dust. Each creature within 5 feet of it must then succeed on a DC 10 Constitution saving throw or be blinded for 1 minute. A blinded creature can repeat the saving throw on each of its turns, ending the effect on itself on a success.

Hrathen please give me a Con Save

Off over to your right over a large sand dune you hear a flurry of shifting sand and a loud thwack.

Do you investigate or move on?

Con save: 21

Hrathen says "I say we move on. This could be dangerous."

"Would you rather whatever that is have the chance to sneak up on us?" Duncan says, looking over towards the dune where they heard the noise. "The desert does not make noises like that naturally, let's see what's out there." He then begins to walk towards the noise, waiting only shortly for the others to join.

As Duncan crests the sand dune he sees 2 giant scorpions locked in combat. The noise came from the the clack of their claws. One is trying to restrain the other with its large claws. Seeing Duncan a scorpion lashes out with its tail with frightening speed onto the sand, causing Duncan to be covered by a wave of sand.

Anyone can roll insight check or nature check to figure out why are they fighting.