Kastix launches his fireball into the darkness, estimating as best he can the 100' range that he thinks Sekkar was indicating from his hissing Draconic. The explosion is audible and the radiant heat can be felt, but the bright flame obscures any view of the target spot, only revealing the sillouhette of Sekkar half-crouched eighty feet away. The lizardman recoils a bit from the flaming ball, only just avoiding the outer perimeter of the conflagration. Moments later the area around Kaylyn, Rhayna, Zeno, Kastix and Pax fills with a thick cloud of greenish fog. It stings their eyes and burns in their throats, and also obscures Sekkar from their view.

Everyone except Sekkar: Take 26 poison damage, or make a DC 14 CON save for half.

Pax is next. Still no visible enemies. Only Sekkar 60-80' away

Kaylyn, Rhayna, D1-4, Zeno, D5, Sekkar, C1, Kastix, D6, Pax

Rhayna CON save: 20

Zeno CON Save: 17

Sekkar's hissing would put a battalion of snakes to a shame "Illusions! The drow were illusion! The mage is hiding behind!" It was still Draconic, just very irritated.

Pax Con save : 20

The black mist around Pax gets eaten away by the poison and she coughs briefly as the poison just stings her skin and eyes a bit. Growling, she backs 10 feet back out of the poison.  She casts Armor of Agathys (at 2nd level), and the black mist around her returns with a surge, sparkles of blue tinging the shadow. (+4 arcane ward hps)

Her sword hisses from it's sheath.

Otherwise, she looks behind her, and all around, trying to spot this mage. She'll move another 5 feet back and ten feet to the north if she can't see anything.  If she spots anything, she moves right at it. 

Kastix 22

Oops. Kaylyn and Rhayna can also take a turn now.

Rhayna casts Daylight at the point where she thought she heard a voice.

Kaylyn Con Save 13

"Sekkar says the drow are illusions, that there is some sort of mage up ahead."  She says as she moves forward 30 feet.  With her darkvision she looks ahead and readies her Eldritch Blast and fires both beams at the mage if it comes into view. 

Attack: 28 Damage: 12

Attack: 21 Damage: 9

Pax moves backwards out of the poisonous cloud, replenishing her protective wards, but still sees no enemies. Kaylyn meanwhile moves forward out of the cloud, ready to attack the first enemy in sight. Suddenly Rhayna's prayer ignites the entire cavern in light, revealing what appears to be nine drow. Kaylyn instinctively fires off her magic blasts at the nearest, a male drow wearing a flowing cloak and grasping a staff, but the blasts pass through the drow harmlessly.

Unfortunately, Rhayna's prayer illuminates Sekkar in bright light, destroying his umbral concealment. Four drow on the perimeter aim small crossbows at the now-visible lizardman and fire.

D1 HXB v Sekkar: Attack: 16 Damage: 4 piercing
D2 HXB v Sekkar: Attack: 15 Damage: 5 piercing
D3 HXB v Sekkar: Attack: 11 Damage: 6 piercing
D4 HXB v Sekkar: Attack: 10 Damage: 4 piercing

If any of the above attacks hit, Sekkar must succeed on a DC 13 Constitution saving throw for each hit or be poisoned for 1 hour. If a saving throw fails by 5 or more, Sekkar is also unconscious while poisoned in this way.

Zeno's turn

Kaylyn, Rhayna, D1-4, Zeno, D5, Sekkar, C1, Kastix, D6, Pax

 (There are markers on the map to represent active spells. The three drow with yellow dots are the ones that aren't firing crossbows or moving at all)

Zeno’s eyes sting with pain from the gas and then the burst of light.  He coughs and retches, then continues to move along, searching for a place to take cover and take a shot.  He glances to the south, considering moving toward the source of that group of attackers, but instead sprints forward to get close to Sekkar, un slinging and loading the light crossbow from his back.  seeing Kaylyn’s shot glass through the first drow, and hearing her cry, he takes aim at the drow near the back, dropping to one knee and firing.

Attack: 12 Damage: 9

Bless to Attack: 3

Zeno's bolt flies true, but glances off one of the metal studs on the drow's leather cuirass. The warrior then runs forward, taking up position beside his illusory duplicate and sliding a spider-patterned shield onto his arm, then draws a shortsword.

Sekkars turn. Map unchanged, except Drow Elite (the real one) is now 35' directly in front of Sekkar.

Kaylyn, Rhayna, D1-4, Zeno, D5, Sekkar, C1, Kastix, D6, Pax

Drow missed. Sekkar made a note of the real warriors, but at the moment was more interested in the mage:

BA: Hunter's Mark for the mage

Handaxe against mage: Attack: 15 Damage: 13  (if hit + 3 )

Crossbow: Attack: 19 Damage: 6 (if hit + 1 )

Run toward the mage full 30ft.

(Question. Are the drows inside the Daylight radius under disadvantage?)

Quote from Wolfy911 >>

(Question. Are the drows inside the Daylight radius under disadvantage?)

(No. Despite its name, the spell doesn't produce actual sunlight. However, the drow shooting crossbows at Sekkar should have had disadvantage due to weapon range, but I forgot. Since they all missed Sekkar anyway, I didn't bother to mention it. I didn't forget with Kaylyn though, so she still got hit.)

The shadows that have been haunting the group for the past several hours were mostly just normal shadows. Mostly. Lurking among them was yet another predator of the deep, and it chooses this moment of confusion to strike at its prey. From the ceiling three dark billowy creatures descend upon Pax and attempt to rake her with their barbed tails while engulfing her in their cloak-like body...

Bite: Attack: 19 Damage: 12 piercing
Tail: Attack: 26 Damage: 19 slashing

If the Bite attack hits... no I don't think it does. Never mind. Of course with the poison cloud in the way, no-one else sees this happen...

Kastix's turn

Kaylyn, Rhayna, D1-4, Zeno, D5, Sekkar, C1, Kastix, D6, Pax

Backing away from the drow and the cloud of neasusus gas, Kastix eyeballs the drow in the light before aiming his staff and casting Scorching Ray, all aimed at the mages, "You want to know how much I hate wasting my fireballs!  Aestu Es!" 

Attack: 17 Damage: 10 Fire Damage

Attack: 24 Damage: 9 Fire Damage

Attack: 12 Damage: 9 Fire Damage 

The reptilian hunter marks his quarry and then throws a well-aimed handaxe. But at the last moment the mage summons a mystical shield and deflects the projective. Kastix also aims his staff and fires his fiery rays. The drow mage is at the uttermost limit of the spell's range, with one ray missing completely and the other striking the magic shield, but the third finds a gap at the bottom and burns the mage's leg through the dark robe. The drow growls in frustration, calling Kastix an "impudent slave" in Undercommon, then casts another spell and vanishes from view! A slight scuff of the feet however is enough to reveal that the drow moved only slightly after his disappearing act.

The poison cloud moves slowly toward Pax, but then suddenly vanishes. Just visible on the edge of Rhayna's light spell, three large creatures can be seen flapping around Pax. With ten-foot wings like the fins of a stingray and long barbed tails, the creatures move in sync with each other, attempting to latch on to Pax's head...

Pax, Kaylyn and Rhayna are all up next...

Kaylyn, Rhayna, D1-4, Zeno, D5, Sekkar, C1, Kastix, D6, Pax

Pax taps her heels together and turns and runs across the room.  In a blur she rushes around the outside of the green poisonous haze and runs up until she's standing right beside the Drow Mage.  

(Bonus action: activate boots of speed.  Speed from 35 to 70.  Movement, 70 feet moved towards the mage. Action, dash, 70 feet rest of the way to the mage.) 

The creature/s that attacked Pax tries to bite her again as she flees... (Attack: 14 Damage: Unable to parse dice roll.)... but she scoots away from the horrid fangs too speedy to be caught. In a blur, Pax runs unnaturally fast across the cavern floor, sprinting past Rhayna, Kaylyn, Zeno and Sekkar, and into the middle of the light.

(140' isn't enough to take Pax all the way to the invisible mage's current position, but can get within 30'. Unless Pax was running to the illusory copy of the mage?)