The booming energy around Xarian's maul rumbles as he deflects the first of the four swarming attacks against him (Arcane Deflection as a reaction, his AC goes from 18 to 20 for one attack, causing the first attack to miss so only 2 of 4 attacks hit him instead of 3 of 4... taking 7 damage instead of 11).

Xarian's reaction resets at the start of his turn.  His owl familiar, Ash, once again flies in the face of a bone creature and flaps her wings, this time the one directly to the north of Xarian, taking the help before flying back to safety 10' behind and above Krizira using Flyby.

Xarian then loops his maul in an uppercut blow against the distracted foe, using Booming Blade.
To Hit:  21
Damage:  12 bludgeoning
Forced Movement:  bone creature is smashed 5' north and upwards into the air (Crusher feat).
Secondary Damage:  if bone creature moves voluntarily, it takes an additional 5 thunder damage (Booming Blade).

"Almost done with them... just a few more," he grunts through gritted teeth.

(Arcane Deflection on the bone creatures' turn meant that Xarian could not use a leveled spell during his turn, which he didn't since Booming Blade is a cantrip.  Now he can use leveled spells again, including Shield as a reaction if necessary).

While the creature's attacks bounce off the scales of her armor, green fire begins to swirl around Sylnora's rapier. She pulls back for another strike, thrusting forwards.

(Action): Green-flame Blade
Attack: 22
Damage: 5

On-Hit: A spiral of green flame whips off the blade, burning the creature behind her target for 3 fire damage.

Three of creature's drop like flies under your collective assault. Richter's longsword cleaves one from shoulder to hip, Xarian's maul implodes the torso of another, and Sylnora's rapier slips through the throat of the third. Green flames burst forth on the other side, burning the monster behind it.

Initiative Order -> Krizira

With Richter dispatching the creature nearest to her, Krizira continues to use her longbow, this time aiming for the creature directly ahead of Sylnora.

(Longbow Attack: 18, Damage: 4)

An arrow flies past Sylnora's shoulder, embedding itself in the torso of the monster right in front of her. It doesn't fall, but between the burns and its new wounds it seems to be struggling to stay on its feet. If the creatures even notice that their numbers have been cut in more than half, they don't seem to care. They continue their attack with a mindless fervor.

Those remaining fill in the gaps in your front line, slashing at three of you up front with their claws.

Action Multi-Attack C(C) against Xarian
Claw Attack: 18
Damage: 3

Claw Attack: 19
Damage: 4

Action Multi-Attack C(M) against Richter
Claw Attack: 7
Damage: 5

Claw Attack: 23
Damage: 6

Action Multi-Attack C(K) against Sylnora
Claw Attack: 7
Damage: 3

Claw Attack: 14
Damage: 3

Initiative Order -> Richter/Xarian -> Sylnora/Krizira

As the claws of the bone creatures scrape harmlessly off his splint armor, Xarian can't shake the idea that perhaps these abominations were once people, the victims of whatever strange cult is at work here.  Turned into thralls of this Lord of Bone...

Ash once again flies in the face of the foe immediately in front of the big man and back to safety, taking the help.  Being preoccupied with his musing about the bone creatures' origin, Xarian does not take advantage of the opening quite as precisely as he has been, his swing a bit sloppier.

Maul with Booming Blade to hit (at advantage due to help):  14
Maul damage:  11 bludgeoning
Crusher Feat - Forced Movement:  bone creature is smashed back 5' north
Booming Blade secondary damage if target moves voluntarily on their turn:  4 thunder

Richter winces as the claws tear into his flesh once more, opening fresh wounds along his arms and torso. He feels a bit of envy as from the corner of his eye he spots the well-armored Xarian goes through another round of attacks unscathed. After this encounter, a trip to an armorer was in his future.

His blade whirls around once more, slicing a wide arc across the monster's chest in front of him.

Action
Longsword Attack: 15
Damage: 9

Sylnora drives her rapier forward again, eager to end the fight now.

(Action): Rapier Melee Attack
Attack: 9
Damage: 11

Krizira again targets the creature directly ahead of Sylnora with her bow. 
(Longbow Attack: 10, Damage: 11) 

Xarian launches another of the monstrosities into the air with his maul, while Richter cuts another down. As Sylnora and Krizira focus in on the last one though, it displays a surprising burst of nimbleness, dodging both of their attacks.

With a screech, it tears into Sylnora with its claws once more.

Action Multi-Attack C(K) against Sylnora
Claw Attack: 19
Damage: 6

Claw Attack: 13
Damage: 4

Initiative Order -> Richter/Xarian -> Sylnora/Krizira

Once again, Ash flies by to take the help action before retreating back to safety up above Krizira.  Doggedly, beginning to breathe hard, Xarian slogs his maul around again, backhand, Booming Blade energy crackling constantly as it crashes into the last bone creature.  His mutter is almost reproachful.

"Stupid bone things need to know when it's over..."  (even though Xarian himself never seems to know when he should stand down).

Maul with Booming Blade to hit (advantage due to help):  24
Maul damage:  11 bludgeoning
Forced Movement due to Crusher Feat:  5' north
Secondary Damage due to Booming Blade if target moves voluntarily on its own turn:  4 thunder

The final creature falls as it's crushed by Xarian's hammer, and once more the cave falls into silence. The bony bodies litter the ground around you, oozing a sludgy brown-red liquid.

"Is everyone alright?" Krizira asks as she moves to the closest fallen creature. She kneals down, examining it closely. (Investigation: 11+2 = 13) 

Xarian grounds his maul and leans on it, catching his breath and trying to make sense of what has just happened.

"Did we... did we just kill what was left of this cult's victims?  Sacrifices to the Lord of Bone?  They went down easily - there were just so many of them.  I mean, we had no choice, but...  well Orlan did warn us."

"You're in bad shape, let me help." Sylnora quickly moves over to Richter, placing a hand on his back. Reaching for the divine power within, she does her best to soothe his wounds (Lay on Hands, 10HP).

"I don't know what those things were, I've never seen anything like them. I think you're on the right track though...If those weren't the kidnapped victims, they were at least summoned from somewhere else or created in some sick ritual."

Richter lets out a shaky breath, bracing himself with a hand against the wall as he feels his wounds start to close. "Thanks for that," He says with a nod to Sylnora. Pushing himself off the wall, he walks around the pile of corpses.

"I'm surprised to find something like this so close. Terrified to think of what might be out there further away from the large cities."

Krizira
You're able to get a better look at the creature now that the fighting has died down. The only vaguely human things about it are that it has two arms and legs and a mouth. There are holes on either side of its head that looks like they might be ears. The bone-line dome that occupies the front of its face and forehead is slightly translucent, and within you can see dark orbs that look like they might be eyes.

If this thing were ever human, elf, or otherwise it has long since been twisted beyond recognition.

Xarian shudders.  The voice (his own) screaming in panic inside his mind hasn't stopped, but he pushes it down and attempts to keep his voice level.

"So, ah... before that little scuffle, we were headed north.  Should we just keep going?"

He tries a casual smile, but the effect is spoiled as he licks his lips nervously, looking around and listening ineffectually for signs of anything else coming.

Xarian Perception:  8

"Well," Krizira says, seeming to think over her words even as she's speaking. "Do you mean to continue on to Kelna or keep exploring these caves? On the one hand, I'd hope we've dealt with most the defenses of this place. On the other, I'd hate to get too deep into this place and have more, or something stronger come after us."  She pauses a moment, "This does seem like it could very well be related to the disappearances though. It seems we should try to learn more." 

"Oh, sorry!"  Xarian looks almost absurdly sheepish in response to Krizira's comments.  "I just meant continue on to the north of this cavern where some of you were going before all these... whatever they are... attacked.  Then there were two other passageways back there..."

He stands there for a moment before continuing in a mumble.  "And... and I doubt we have dealt with most of the defenses here.  Seemed too easy.  Not that it actually was easy," he adds hastily, looking at Richter's nasty, partially healed wounds, along with his own, somewhat more minor injuries.

"I had almost forgotten about Kelna.  My fault.  But our job is to investigate and... I don't think we know what we're looking at yet here in these caves."