Ordrin draws the glowing mace back to strike at the boneless horror when out of the corner of his eye he catches sight of Riris. She looks like a different person, closer in form to Mormesk even than to herself. With a chilling realization of her peril he sheathes the mace, turns away from the boneless thing and charges at Mormesk. At the same time, he calls on the holy grace of Sharindlar, digging deep within himself and bestowing her protection upon Riris. As Ordrin struggles to reach Mormesk in time, the spectral form of Firnat dissolves and flows through the air to Riris, gathering around her into a a barely perceptible shell. 

Movement in a straight line as far as he can toward Mormesk.

Action Shield of Faith cast on Riris - +2AC

Bonus action Harness Divine Power to regain one 1st level spell slot

 

(To Hyakujo: As I said before, sticking by RaW(Rules as Written) regarding spell economy. Which would mean you couldn't use HDP and SoF in the same turn, as both require a bonus action. At this point I'll interpret that your main intentions are to grant Riris at least some level of protection, so I'll assume you dash as your action, as well grant Riris SoF as the final interpretation of Ordrin's actions for the turn. You also still have Spiritual Weapon up as it is not a concentration spell, and Harness Divine has since been refunded.)

Rc-Boneless Attack of Opportunity:
Slam vs Ordrin(AC 20) - Attack: 9 Damage: 7 nonmagical bludgeoning. 

Following the End of Ordrin's Turn:
Mormesk Legendary Action: Enervating Grasp vs Charlotte(AC 15) - Attack: 11 Damage: 20 cold damage.
Target speed is reduced by 10ft until the end of their turn. Target also cannot be healed until the start of Mormesks' next turn. 
(Any conc. save and adjustments to be addressed in PM) 

Lair Action: Feast on Life
All Creatures within 10ft of Boneless and Mormesk (excluding their allies) must make a DC 11 Con Save or take 1 Necrotic Damage.
(ie. Mixum, Charlotte, Riris, and Ordin)

Ma: K16.
Ac-Boneless Multi-Attack:
Slam vs Mixum(AC 17) - Attack: 22 Damage: 6 nonmagical bludgeoning. 
Slam vs Mixum(AC 17) - Attack: 24 Damage: 4 nonmagical bludgeoning. 
If both hit, Ordrin is considered Grappled. 

Following the End of Boneless's Turn:
Mormesk's Last Legendary Action: Enervating Grasp vs Ordrin(AC 20) - Attack: 10 Damage: 16 cold damage.
Target speed is reduced by 10ft until the end of their turn. Target also cannot be healed until the start of Mormesks' next turn.

As Ordin prepared to strike what might be the final blow against the boneless creature, his attention is drawn back to Riris' far more frail and somehow smaller looking frame compared to the looming darkness that was Mormesk. At the chilling realization that the wizard intended to pick off the others one by one, the mace is put away as he charged to her side, heedless of the danger of the Boneless creature striking as he retreated. He would go on to push himself to the limit in fighting against the unholy "mire" to make the journey, and in recalling some of Firnat's essence, he'd direct it surround Riris' in a protective shield. Only Firnat's weapon remained floating in the air, ready to be used at a moment's notice.

"Tch! More protections? Fine then!" Mormesk whipped around to Ordrin with his hand raised as if to backhand Ordrin. Yet when it comes down, it is instead swept at and through Charlotte, potentially rendering it inert as even the constructs power source is drained from contact. "I guess I'll just have to rip them apart! One. By. One." 

Lair Action: Once more the ground and atmosphere seems to settle and revert back to normal. Knowing what was to come next, those closest to the boneless and wraith alike brace themselves as whatever unearthly magic saturated the place sought to crush the very life from then, and pass it on to their undead foes.

After which, the distant sound of fighting to the north finally seems to come to a close, as the groans and vaguely familiar battle cries ceases to echo from the north. While the party can't be sure of the exacts on what's been going on, it seems for the moment that the Undead Reinforcements(N) have at least been stemmed for the moment.

The Boneless mass practically tears itself apart to move with an unnatural speed towards the next closest mortal. It's ongoing cackling sounding pained with every advancing step. And yet without remorse or hesitation, the nightmarish thing would spring up on bloody hands to try and kick and wrap itself around it chosen prey: Mixum.

"Now for you." Mormesk states as he lunges next for Odrin's head with a skeletal hand that appeared to almost grow unnaturally to try and grip the entirety of the dwarf's head, only to phase right through and disrupt something far more vital within if Ordrin's defenses fail him. 

Pip now up! 

Initiative Tracker(Round 5):
Lair Action - 20
Undead Reinforcements(N) - 20 (Defeated?)
Boneless - 20
Shadow Wolf - 16(Defeated)
Pip - 11
Mormesk - 11
Riris - 6 (Under Shield of Faith)
Mixum - 3 (Bardically Inspired)
Keleton - 2(Defeated)
Undead Reinforcements(S) - 1 (Appearing in 1)
Ordrin - 0 (Concentrating on Shield of Faith)

Key: 

M=Mixum
O=Ordrin
P=Pip
B=Boneless
K=Keleton
S=Shadow Wolf
R=Riris
E=Mormesk
U=Undead Reinforcement
D=Undead Reinforcement

 Updated Map:

 

Ordrin CON: 20

Riris's Constitution Save: 19

Pip, seeing the boneless is nearly dead, wants to make sure he finishes it off and does not want to miss.

Three glowing darts of magical force then slam into the boneless for 11 force damage. Magic Missile

If the creatures does in fact die he then moves north as much as he can towards the door as he fumbles in a pocket.

Con save. 19

Start of Mormesk's Turn: Legendary Actions refreshed.

Ac-Mormesk Life Drain:
Life Drain vs Ordin(AC 20) - Attack: 25 Damage: Unable to parse dice roll. Necrotic Damage. Con Save[DC 14] or hit point maximum reduced by same damage damage. Additionally, hp cannot be restored until the start of Mormesk's next turn.
Also if hit, make a concentration saving throw.

 
Pip unleashes dart after dart of arcane force the boneless' mass' way and blows off chunks of flesh left and right. But to his horror or annoyance or even a combination of the two, the thing picks itself back off the floor on shaky limbs and sends a wide, toothless smile the gnome's way.

Mormesk turns more fully to Ordrin; untouched since the fight began, and yet radiating an even greater anger, frustration, and malice the cleric's way. "Foolish dwarf. You should've waited until I was done with your friends. But now it is your turn to suffer." As he raises his bony hand for a punch, the spirits that had been floating about him groaning and wailing their limit are drawn into the skeletal appendage for a brief few moments, lighting up it up in a dark light just before he brings life draining fist down!

Riris & Mixum now up! 

Initiative Tracker(Round 5):
Lair Action - 20
Undead Reinforcements(N) - 20 (Defeated?)
Boneless - 20
Pip - 11
Mormesk - 11
Riris - 6 (Under Shield of Faith)
Mixum - 3 (Bardically Inspired)
Undead Reinforcements(S) - 1 (Appearing in 1)
Ordrin - 0 (Concentrating on Shield of Faith)

Key: 

M=Mixum
O=Ordrin
P=Pip
B=Boneless
K=Keleton
S=Shadow Wolf
R=Riris
E=Mormesk
U=Undead Reinforcement
D=Undead Reinforcement

 Updated Map:

 

Riris, after being put in a very tight spot, marches on with her usual panache. Taking a short look around, she finally finds her way out. Rapier drawn, she aims it onto Mormesk's legs, trying to get a distraction even if it doesn't come out as a clean hit.

Attack: 7 Damage: 13 (Non-Magical) Piercing

Regardless of the actual success of her attempt, she uses her incredible speed to circle around Mormesk and escape northward through the gap her attack created. After finally reaching her destination of N15, she looks back towards Ordrin, and raises her fist as she inspires him. "Thank ya for the help! Now ya just gotta keep going!" (Second use of Bardic Inspiration.)

Mixum spins around and sees the boneless mass advancing upon him. He raises the crossbow and fires twice. 

attack  11

damage  7

attack  24

damage  9

He readies a shield reaction if the boneless appears to hit him. Charlotte readies to defend Riris or Odrin from Mormesk. 

edit.

 1   from the crit.

Following the End of Mixum's Turn:
Mormesk Legendary Action: Enervating Grasp vs Charlotte(AC 15) - Attack: 8 Damage: 14 cold damage.
Target speed is reduced by 10ft until the end of their turn. Target also cannot be healed until the start of Mormesks' next turn. 
(Any conc. save and adjustments to be addressed in PM) 

Riris aimed for where she thought Mormesk's legs to be under the cloak. But where she failed in finding her mark, a flustered Mormesk trying to keep his robe instinctively closed from all of her flourish did afford her an opportunity to slip away. To the backdrop of the undead shaking a fist her direction after, some words of encouragement are thrown Ordrin's way for good measure!

Mixum spins and in a flurry of crack shots managed to put down the Boneless mass once and for all, but only further fluster Mormesk further with a narrow miss of the second shot. A small set back, or so the gnome could assure himself as Charlotte once more appeared to ready herself to defend the only other living ally nearby at the time.

"Oh no you don't! I have had quite enough of you!" Mormesk shouts as he abruptly lashed out for Charlotte once more in a desperate attempt to at least put down one foe. 

Come what may of his efforts, the billow ghost flames that seemed to make up some of his being dim as the clattering sound of bones began to echo loudly just outside the door. "Ah! Ahahaha! Finally you lazy bones are here! Get them! Leave none alive to trouble your master further!" He cackled as four skeletons coming rushing to the doorway, waving around rusted blades, bent metal cudgels, and garbed in the tathered dregs they may have worn in life. Worst of all, it sounded even as more yet were just outside. The Undead Reinforcements(S) had finally arrived on the scene.

Ordrin turn is now up! 

Initiative Tracker(Round 5):
Lair Action - 20
Undead Reinforcements(N) - 20 (Defeated?)
Boneless - 20
Pip - 11
Mormesk - 11
Riris - 6 (Under Shield of Faith)
Mixum - 3 (Bardically Inspired)(Charlotte Auto Dodge.
Undead Reinforcements(S) - 1
Ordrin - 0 (Concentrating on Shield of Faith, Bardically Inspired)

Key: 

M=Mixum
O=Ordrin
P=Pip
B=Boneless
K=Keleton
S=Shadow Wolf
R=Riris
E=Mormesk
S=Undead Reinforcement

 Updated Map:

 

For the moment, at least, Ordrin's focus cannot be interrupted. He and the spiritual Firnat strike in the name of Moradin.

Ordrin attack on Mormesk: 19, damage: 5

Spiritual Weapon attack on Mormesk: 20, damage: 11

Following the End of Ordrin's Turn:
Mormesk Legendary Action: Enervating Grasp vs Charlotte(AC 15) - Attack: 7 Damage: 16 cold damage.
Target speed is reduced by 10ft until the end of their turn. Target also cannot be healed until the start of Mormesks' next turn. 
(Charlotte's Deflect reaction already accounted for in above rolls) 

Lair Action: Dreadful Mire
Non-Undead Creatures have their movement speed halved and receive half-healing.

Ordin & Firnat try to strike in a pincer maneuver; a call to the All Father Moradin going out as they struck in a righteous fury. Yet both blows are battered aside a sweep of the wraith's robe. "Nice try, dwarfs! But it'll take more than-" He freezes up suddenly and looks down to his robe, drawing attention to the rapidly disintegrating edges. Those with sharp eyes would know it to be teh same spot where Ordin's radiant mace had made contact.

"Th-this changes nothing!" Mormesk called out as he whipped out a bony hand the Cleric's way and drawing both Charlotte's ire and intervention, much to wraith's infuriation.

Lair Action: The stonework around and even the air begins to take on the qualities of a quagmire once more, actively and angrily clawing up at the legs of anyone not of the undead.

Pip turn is now up! 

Initiative Tracker(Round 6):
Lair Action - 20
Undead Reinforcements(N) - 20 (Defeated?)
Pip - 11
Mormesk - 11
Riris - 6 (Under Shield of Faith)
Mixum - 3 (Bardically Inspired)(Charlotte Auto Dodge.
Undead Reinforcements(S) - 1
Ordrin - 0 (Concentrating on Shield of Faith, Bardically Inspired)

Key: 

M=Mixum
O=Ordrin
P=Pip
B=Boneless
K=Keleton
S=Shadow Wolf
R=Riris
E=Mormesk
S=Undead Reinforcement

 Updated Map:

 

 .

Pip creates a shard of ice and flings it the top right undead that entered the room.  Hit or miss it explodes with shards of ice hitting it and the other minions close to it.

Ice Knife Attack: 18 Damage: 7 piercing

Dex save DC14 or 7 cold

It should explode and hit all 4 by the door.

Following the End of Pip's Turn:
Mormesk Legendary Action: Enervating Grasp vs Charlotte(AC 15) - Attack: 25 Damage: 15 cold damage.
Target speed is reduced by 10ft until the end of their turn. Target also cannot be healed until the start of Mormesks' next turn. 

Skelly #2 Dex Save vs Pip: 19.
Skelly #3 Dex Save vs Pip: 5.
Skelly #4 Dex Save vs Pip: 12.

Start of Mormesk's Turn: Legendary Actions refreshed.

Ac-Mormesk Life Drain:
Life Drain vs Ordin(AC 20) - Attack: 24 Damage: 25 Necrotic Damage. Con Save[DC 14] or hit point maximum reduced by same damage damage. Additionally, hp cannot be restored until the start of Mormesk's next turn.
Also if hit, make a concentration saving throw.

 
Pip acts decisively and swiftly in turning what little moisture in the air there was into a shard of explosive ice, and with a quick gesture, sends it flying for the skeletons at the door. But while most if not all there would fall, the wizard could not allow himself to feel at ease knowing yet more awaited the group just outside.

"Curse you, Gnome! I knew I should've finished you first!" Mormesk yells. "And out of my way you mechanical monstrosity!" He adds as he swipes once more at the Charlotte's head, readily freezing everything within if contact is yet made.

Mormesk then clicks what by all accounts should be a nonexistent tongue. "Still! If you think destroying my minions, I would have you all think again!" With that cryptic warning given, he sets his apparent sights once more on Ordrin. "As for you, bearded one. That does /NOT/ belong to you!"  He shouts as he lunged forth again for Ordrin with a wild haymaker for the jaw.

Mixum and Riris' turns are now up! 

Initiative Tracker(Round 6):
Lair Action - 20
Undead Reinforcements(N) - 20 (Defeated?)
Pip - 11
Mormesk - 11 (Conc. on Spirit Shroud.)
Riris - 6 (Under Shield of Faith)
Mixum - 3 (Bardically Inspired)(Charlotte Auto Dodge.
Undead Reinforcements(S) - 1
Ordrin - 0 (Concentrating on Shield of Faith, Bardically Inspired)

Key: 

M=Mixum
O=Ordrin
P=Pip
B=Boneless
K=Keleton
S=Shadow Wolf
R=Riris
E=Mormesk
S=Undead Reinforcement

 Updated Map:

 

Mixum moves south (L 19) and focuses his shots on Mormesk. 

attack 17   damage  8

attack 15   damage  8

Charlotte will  dodge and continue to use her reaction protect Odrin. (OOC: did Charlotte take any damage ? )

Riris doesn't make any moves from her position, seeing it as perfect for what she was about to do. From her rapier, she shifts to her lute, and strums a lousy note that soon gets overshadowed by the loud kaboom that comes from her casting Shatter centered directly against the wall south of Mormesk.

(OOC: I don't know how we do these area of effects, exactly, but I counted Mormesk as 10 feet away from the wall, and the AoE for Shatter is a 10-feet radius sphere, so it should work right, right?)

Constitution Save DC 13 against 17 Thunder damage, halved on a success.

Mormesk's Constitution Save vs Riris(DC 13): 11.

Rc-Mormesk: Casting Shield vs Mixum's Attacks, raising AC to 21.

Following the End of Mixum's Turn:
Mormesk Legendary Action: Enervating Grasp vs Charlotte(AC 15) - Attack: 8 Damage: 6 cold damage.
Target speed is reduced by 10ft until the end of their turn. Target also cannot be healed until the start of Mormesks' next turn. 

Ma-Undead Reinforcements(S): Into the room.
Ac-Undead Reinforcements(S):
Picks & Improvised Weaponry vs Riris(17) - Attack: 7 Damage: 3 Nonmagical bludgeoning.
Picks & Improvised Weaponry vs Mixum(17) - Attack: 5 Damage: 4 Nonmagical bludgeoning.
Picks & Improvised Weaponry vs Mixum(17) - Attack: 15 Damage: 6 Nonmagical bludgeoning.
Picks & Improvised Weaponry vs Mixum(17) - Attack: 10 Damage: 5 Nonmagical bludgeoning.
Picks & Improvised Weaponry vs Ordrin(20) - Attack: 24 Damage: 9 Nonmagical bludgeoning.
Picks & Improvised Weaponry vs Ordrin(20) - Attack: 10 Damage: 6 Nonmagical bludgeoning.

Riris in breaking out the lute once more unleashes such a loud kaboom that it would echo throughout the cavern beyond the room. Just as she surely rattled whatever Mormesk and Mormesk alone had for bones, as the entity is left clutching at nonexistent ears and howling in pain. "You wretched little halfling! I'll have your--" But his words are cut off at the twang of a crossbow.

Mixum cranks out shot after shot of his modified hand crossbow once more and is again denied success in a sharp word from Mormesk causing another arcane barrier to spring up in his defense. Yet knowing the spirit couldn't keep it up forever is a comfort, if but a cold one. Charlotte remains on the defensive and on look out for any opportunity to intercede again.

Thoroughly aggravated, Mormes start to lurch forward in the direction of Mixum, but changes his mind at the last moment in an attempt to rake bony hands through her metallic carapace.

The remaining Undead Reinforcements(S) surge into the room, and using everything at their disposal, be it rusted weaponry or old heavy rocks as projectiles, they attack in a blind flurry at just about everyone in the room still alive and kicking!

Ordin turns is now up! 

Initiative Tracker(Round 6):
Lair Action - 20
Undead Reinforcements(N) - 20 (Defeated?)
Pip - 11
Mormesk - 11 (Conc. on Spirit Shroud.)
Riris - 6 (Under Shield of Faith)
Mixum - 3 (Bardically Inspired)(Charlotte Auto Dodge.
Undead Reinforcements(S) - 1
Ordrin - 0 (Concentrating on Shield of Faith, Bardically Inspired)

Key: 

M=Mixum
O=Ordrin
P=Pip
B=Boneless
K=Keleton
S=Shadow Wolf
R=Riris
E=Mormesk
S=Undead Reinforcement

 Updated Map:

 

Ordrin is slammed forward by the attack from undead creature. A painful grimace is replaced by a grim smile as Firnat's armor holds strong. He looks to her spectral form, nodding at it as if it is really her and not the unworldly manifestation that it is. She returns his look with a smile and he is left wondering how, as she produces a spectral hammer and whirls it into Mormesk with all the grace and might of her corporeal self. Ordrin does not miss his opportunity, swinging into Mormesk to meet her hammer's head with Lightbringer.

Ordrin attack with Lightbringer: Attack: 25 Damage: 6

Spiritual weapon attack: Attack: 25 Damage: 16

Bonus Radiant Damage from Light Bringer vs Mormesk: 4.

(Forgot Mormesk needed to make a Concentration save vs that shatter before, so adding that in now as well.)

Mormesk's Concentration Save(DC 10): 17, 15.

Following the End of Ordrin's Turn:
Mormesk Legendary Action: Enervating Grasp vs Ordrin(AC 20) - Attack: 18 Damage: 19 cold damage.
Target speed is reduced by 10ft until the end of their turn. Target also cannot be healed until the start of Mormesks' next turn. 
(Charlotte's Deflect reaction already accounted for in above rolls) 

Lair Action: Feast on Life
All Creatures within 10ft of Boneless and Mormesk (excluding their allies) must make a DC 11 Con Save or take 4  Necrotic Damage.

Despite some intent to keep to a coordinated strike, neither Ordin or Firnat had fully expected for Mormesk to reel back so violently after Lightbringer squarely shrug the spirit's side, releasing a small explosion of divine energy and light. Yet the spook nearly rag dolled away under the force of the blow.

A near animalistic screech fills the air as Mormesk leaps back off the ground to lash out at Ordrin with reckless abandon and heedless of Charlotte's attempts to dissuade him.

 Lair Action: Once more the ground and atmosphere seems to settle and revert back to normal. Knowing what was to come next, those closest to the boneless and wraith alike brace themselves as whatever unearthly magic saturated the place sought to crush the very life from then, and pass it on to their undead foes.

From somewhere towards the north, the group can just make out what sounds like heavy booted feet beginning to make their way to the group.

Pip turn is now up! 

Initiative Tracker(Round 7):
Lair Action - 20
Undead Reinforcements(N) - 20 (Defeated?)
Pip - 11
Mormesk - 11 (Conc. on Spirit Shroud.)
Riris - 6 (Under Shield of Faith)
Mixum - 3 (Bardically Inspired)(Charlotte Auto Dodge.
Undead Reinforcements(S) - 1
Ordin - 0 (Concentrating on Shield of Faith, Bardically Inspired)

Key: 

M=Mixum
O=Ordrin
P=Pip
B=Boneless
K=Keleton
S=Shadow Wolf
R=Riris
E=Mormesk
S=Undead Reinforcement

 Updated Map:

 

Riris Constitution Save: 5