Petmailer, much more alone on the stairs now, readies his bow, while Stena has hers readied angling back up the stairs for when the ghosties return.

Lia quivers in confusion, but seems to shake whatever had her so befuddled off handily.

Initiative:
Neth: 23 (Readied EB)
Stena: 22    (Readied arrow)
Petmailer: 20    (Readied arrow)  
Lia: 20 
Cows: 19
Yuk Yuk: 19 (readied dagger throw) (up the stairs)
Spiderbait: 14 (readied dagger throw) (up the stairs)
Kolose: 13  (Ready to Toll)  <------<<<
Galingal: 12  <------<<<
Fargas: 12 (readied hand crossbow) (up the stairs)
Jimjar: 8 (readied hand crossbow) (up the stairs)
Coffin Residents: 7 (No longer Turned/No longer Turned/X/X) 

Not knowing where the wraiths will appear again, Galingal decides to keep moving forward to get out of the fog and take in the circumstances of the tomb, his rapier at the ready.  

Galingal is able to clamber over unmoving cow carcasses in the fog, eventually emerging in the doorway. There are an additional three dead cows in the middle of the room, showing signs of having been savaged by the spectral undead, and the room is actually brighter than before, as the far right corner is covered in flames that look to be originating from shattered shards of one of the crystals. The cows weren't put down before they made an absolute wreck of the place, smashing the urns, overturning the assorted offerings or decorative items, the lid of the far left coffin being cracked, and a few stray cow plops having been kicked and tracked all over, adding their pungent aroma to the burning hair of the cow closest to the flames. 

That's what Galingal takes in at a glance, as he whirls to face the fog right behind him, rapier held to thrust at any who charge him.

Initiative:
Neth: 23 (Readied EB)
Stena: 22    (Readied arrow)
Petmailer: 20    (Readied arrow)  
Lia: 20 
Cows: 19
Yuk Yuk: 19 (readied dagger throw) (up the stairs)
Spiderbait: 14 (readied dagger throw) (up the stairs)
Kolose: 13  (Ready to Toll)  <------<<<
Galingal: 12 (Readied rapier)
Fargas: 12 (readied hand crossbow) (up the stairs)
Jimjar: 8 (readied hand crossbow) (up the stairs)
Coffin Residents: 7 (No longer Turned/No longer Turned/X/X) 

Kolose struggles, seeing so many fallen behind still, really wanting to get out of the range of the dangerous crystals... But eventually, he moves back down a bit again. Still keeping a toll ready, just in case.

"Are they fighting down there..? I thought we were doing a tactical retreat..!"

((There are still more crystals on the stairs as well, just as a reminder.))

Kolose descends until he can get visual on Lia and Petmailer, but he doesn't spot Stena or Galingal.

He doesn't have long to wait as a spectral undead emerges from the wall directly adjacent to Petmailer, and another emerges where Stena was, looking about for the dwarf.

((Stena, Kolose and Petmailer can all take their readied actions. Petmailer's will be either be with 3/4 cover or disadvantage, depending on if he would opt to shoot as soon as any part of it emerged from the wall, or shooting when it is next to him. Once you've taken any readied actions, the undead will finish their turn.))

Initiative:
Neth: 23 (Readied EB)
Stena: 22    (Readied arrow)
Petmailer: 20    (Readied arrow)  
Lia: 20 
Cows: 19
Yuk Yuk: 19 (readied dagger throw) (up the stairs)
Spiderbait: 14 (readied dagger throw) (up the stairs)
Kolose: 13  (Ready to Toll)
Galingal: 12 (Readied rapier)
Fargas: 12 (readied hand crossbow) (up the stairs)
Jimjar: 8 (readied hand crossbow) (up the stairs)
Coffin Residents: 7 (No longer Turned/No longer Turned/X/X)   <------<<<

Attack: 8 Damage: 9 

 ((I rolled without advantage guessing Stena is lit up, otherwise 15 ))

((Yes, the area has the soft glow of faerie fire.))

Stena's bow string catches on a cow hoof, and the arrow clatters at her feet. The undead swirls and descends on her.

Petmailer’s readied action goes off, when he sees the ghost emerge, he shoots his bow immediately.  “I don’t like this, little help?  Anyone able to hit this thing?”  The bowstring twangs and his arrow seems to strike true, but passes through…

Long bow : 18 to hit, for 7 points of piercing damage.

Kolose curses first normally, and then in a far more potent way as he tolls the one ghost he can see.

6 

(Wasn't sure if it was already injured or not, so... adding 1d5-1 should be equivalent to rolling a d12 right?)

4 

((Not equivalent, since you're rolling two die, increases odds of getting middle numbers. If you're not sure in the future, you can roll both and I'll use the applicable one.))

Wis: 20

Petmailer's arrow leaps from his bow, shattering in the stone as it hits the spectre in the face, shards of arrow slowed slightly as they scatter out through the incorporeal visage. 

Kolose unleashes his held spell, the magic of this place surging around him, but the target of his spell seems to shrug it off. 

84

((Kolose, roll two 1d8s for me please, as separate rolls.))

7

1

There is a resounding boom that thunders through the tomb as Kolose vanishes before popping out half a flight up, pinned against the wall. He feels like the magic wants to take him further, but was constrained by how far he could see as it lets him drop to the ground. Lia and Neth are caught in the blast where the wizard vanished from, trying to clap their hands over their ears and weathering the booming magic.

Lia: 5
Neth: 3

16

The aasimar and the tiefling are swaying on their feet, blood running from their ears and noses.

The undead swarm at Petmailer and and Stena, attacking before vanishing through the walls again.

Attack on Petmailer: 23 Damage: 8 necrotic, and DC 10 CON Save

Attack on Stena: 20 Damage: 11 necrotic, and DC 10 CON Save

Initiative:

Neth: 23 
Stena: 22      <------<<<
Petmailer: 20     <------<<<
Lia: 20 
Cows: 19
Yuk Yuk: 19 (readied dagger throw) (up the stairs)
Spiderbait: 14 (readied dagger throw) (up the stairs)
Kolose: 13 
Galingal: 12 (Readied rapier)
Fargas: 12 (readied hand crossbow) (up the stairs)
Jimjar: 8 (readied hand crossbow) (up the stairs)
Coffin Residents: 7 (No longer Turned/No longer Turned/X/X) 

Neth curses and staggers past Lia, heading down the stairs, "We need to finish them before we blow ourselves up with our own magic!"

Neth: 23 (readied dagger)
Stena: 22      <------<<<
Petmailer: 20     <------<<<
Lia: 20 
Cows: 19
Yuk Yuk: 19 (readied dagger throw) (up the stairs)
Spiderbait: 14 (readied dagger throw) (up the stairs)
Kolose: 13 
Galingal: 12 (Readied rapier)
Fargas: 12 (readied hand crossbow) (up the stairs)
Jimjar: 8 (readied hand crossbow) (up the stairs)
Coffin Residents: 7 (No longer Turned/No longer Turned/X/X) 

Petmailer is near death, reeling.  He disengages and moves up 30 feet, heading up the stairs, putting his bow away as he does, his hand moves to his short sword, drawing it out.  “Going to die, I feel terrible…”

Con Save : 16

Con save: 8 (23)

Stena stiffens as the ghost's hand clutches inside her chest.

As it flees she is left shuddering, barely standing. She'll look up the stairs briefly before taking a step back into the fog moving to where she thinks the grey elf is,

"Galingal. Aye need ye."

She readies another arrow.