Keyleth CON Save: 6

Varan CON save 15

Between the cold blast and the sword attack, Keyleth collapses to the ground, unconscious.

Avarice Con save: 17

Wulgar con save :  30 

Wulgar wisdom save with the hit : 12 

Mulligan save vs DC 17 Con:  22

((I think Headless Ragna's first attack was supposed to be at disadvantage but *shrug*))

     As a bonus Action, Mulligan calls out "Get up, Keyleth, your time hasn't run out yet!" and casts a Healing Word her way for 7 healing.

     Mulligan will move about 30' straight down to get into range of Headless Ragnar and chuck a couple of daggers at him.

First Dagger Attack:  Attack: 18 Damage: 10 plus 1 to attack roll from Bless

Second DaggerAttack:  Attack: 29 Damage: 11 plus 3 to attack roll from Bless

And of either hit I will use Defensive Flourish on the first hit to add 8 to the damage and my AC until the start of my next turn...

Avarice continues to blast Headless Ragnar with three beams of purple crackling force.
Eldritch blast: 16 Force: 9
Eldritch blast: 13 Force: 8
Eldritch blast: 27 Force: 9

Varan is unable to shake of the cold and he is chilled to the bone.  

He draws his crossbow and fires off a bolt at Headless Ragnar.  Attack: 27 Damage: 9

"This is going to be a grind!" he shouts.  "We've barely scratched the surface of this battle!"

Wulgar is just pure angry at the false Ragnar, giving a fierce roar and giving all party members advantage on attacks and saving throws for the next round with his Zealous Presence.  He begins swinging his great axe twice at him with renewed courage.  (Adv cancelling out disadvantage from prior effect.)

Great axe one : Attack: 20 Damage: 16 

Greate axe two : Attack: 21 Damage: 30 

Divine fury necrotic damage with first hit : 11 

Keyleth staggers to her feet after her brief unconsciousness. "Thanks," she calls to Mulligan, then runs the rest of the way to the drowned Wulgar and slashes at him.

Main hand attack: 24 Damage: 10 piercing
Offhand attack: 14 Damage: 4 piercing
Sneak attack: 30 piercing

While Keyleth falls, a word from Mulligan grants her the energy to continue to fight. Both of Mulligan's daggers sink through the dead knight's armor. 

Two of Avarice's blow rebound off Ragnar's shield, but one crackles directly into its chest. 

Varan's cloudkill continues to move, catching the drowned Wulgar in the choking fog. DC18 Con save: 10 - though the frozen, teeth-chattering duplicate of Wulgar manages to resist the blast better this round, the being claws its throat and crumples to the ground, slain. Varan's bolt lodges firmly into the headless Ragnar's chest. 

The true Wulgar's roar echoes through the grandfather clock's circular rooms and - presumably - beyond into the enormous, oversized room you can barely see at the edges of your vision, the headless knight still parries both of Wulgar's blows. 

(Keyleth: Drowned Wulgar perished in the Cloudkill, so I assume you're targeting the headless Ragner this round and I'm using the rolls you've already made. Let me know if you would've done something different.)

One of Keyleth's strikes misses, but the other slips under the headless Ragnar's plate and directly into the undead's ribs. 

The true Ragnar gives a shout, lifting his blade into his air - slicing down twice towards his duplicate. 
Ragnar Attack (Headless Ragnar): 20 Damage: 10 plus 5 cold plus 3 radiant. 
Ragnar Attack (Headless Ragnar): 11 Damage: 10 plus 1 cold plus 7 radiant. 
Both blows are neatly deflected by the figure's sword. 

The decapitated head gives a laugh, the desiccated flesh twisting in a hideous display of amusement. "And this is what you are, Ragnar? Weak? Pathetic? You were always too proud of yourself - one year passed, and the fools you ruled over finally recognized you for who you were. Nothing. Your palace was stormed, your shoulders lifted from the burden of your neck - and now, here we are."

Headless Ragnar Bonus Action: staggering smite
Headless Ragnar Action: Attack
Headless Ragnar Attack (Ragnar): 26 Damage: 13 plus 15 necrotic. 
Headless Ragnar Attack (Ragnar): 13 Damage: 9 plus 19 necrotic. 
Headless Ragnar Attack (Wulgar): 25 Damage: 6 plus 20 necrotic. 
The first target to be hit takes an additional 11 psychic damage and must make a DC 18 Wisdom saving throw or suffer the effects of staggering smite. 
Ragnar DC18 Wisdom saving throw: 27 - Ragnar shakes off the impact of the spell and both blows, but he still remains heavily bleeding. 

Even as the headless Ragnar winds up for another round of strikes, it suddenly freezes, encased in temporal energy as you find yourselves dodging the rapidly-shifting clockwork arms sweeping across the arena. 

What time is it? 10
Tick, tock: 4

The chain-wielding Avarice reanimates, as does the summoned Erinyes at his side. Meanwhile, across the map, the feathered-wing version of Avarice also unfreezes; the latter takes to the sky, strangely donning robes akin to a priest. When the celestial-inspired Avarice speaks, his voice resounds through your minds, righteous and suffused with internal might. 

"Is this what you want to become, Avarice? Wretched, slaving for gold and power until you forget who you once were?" the being spoke, casting a judgmental glare over the true Avarice. "I am your ally, Avarice. I am what you could become - greed and lust for power shrouds your mind, yet you are so blind to realize the only method of attaining your own is to abandon the principles you live by now." An aura of warmth surrounds the celestial, who makes no move to reach for any weapons nor speaks the incantations to any spells. 

"So aid me then in surviving this trial! If I die here your lofty speech has been in vain." Avarice calls out to his better self.
Then Avarice turns on his still hexed worse self and blasts it with three beams of purple crackling force.

Eldritch blast: 26 Force: 10 Necrotic: 4
Eldritch blast: 14 Force: 11 Necrotic: 3
Eldritch blast: 14 Force: 10 Necrotic: 5

     Mulligan rushes due west into combat with newly unfrozen Avarice.  Drawing his rapier, Mulligan get's all fancy with it as he's finally in range to dance with his blade... 

Rapier Attack: 25 Damage: 12   plus 2 to Attack due to Bless

Rapier Attack: 20 Damage: 15   plus 2 to Attack due to Bless

First attack to hit also does 21 in Sneak Attack Damage

And if either hit, Mulligan will again use Defensive flourish to add 4 to that attack's damage, plus his AC until start of next round...

"This guy..." Varan mutters as the hell-bound Avarice starts moving again. 

He loads a crossbow bolt but moves over to Keyleth.  "Make what use of this you can, Explorer."  Varan drops concentration on the cloudkill and instead casts greater invisibility on Keyleth.

He is also prepared to counterspell the devil-Avarice at 4th level with his reaction, if necessary.

Now that headless Ragnar is frozen again, Wulgar steps away 3 steps west and one step north, attacking faux Avarice.  He swings his great axe hard at him.  

Great axe slice 1 : Attack: 19 Damage: 21 

Great axe slice 2 : Attack: 15 Damage: 19 

Divine fury damage (on first hit) : 10 

Keyleth grins as she's turned invisible, makes a mental note to thank Varan later, and slices at the headless Ragnar.

Main hand attack: 23 Damage: 8 piercing
Offhand attack: 21 Damage: 5 piercing
Sneak attack: 27 piercing

(just realized I was supposed to roll with advantage, lemme roll again)

Main hand: 32
Offhand: 20

(that's a crit for the main hand attack, so an additional 6 piercing damage)

(plus crit sneak attack for an additional 20 piercing damage)

One of Avarice's blasts connect with the Kyton. Mulligan and Keyleth fare better, and one of Wulgar's strikes hits - the Kyton visibly staggers, clearly heavily injured. 

Mulligan, as your strike hits the Kyton, a searing flash of fire erupts from your blade - make a DC 18 Dexterity saving throw or take 35 fire damage, half on a success. 

Ragnar lays a hand over his wounds, sealing them with a flash of healing - Healing Hands 45 on self. 

The Chain Devil's chains whip around in a frenzy! 
Chain Attack (Mulligan): 8 Damage: 5
Chain Attack (Keyleth): 24 Damage: 9
Chain Attack (Ragnar): 24 Damage: 12
Chain Attack (Wulgar): 26 Damage: 8
Upon a hit, make a DC 13 Wisdom saving throw or be frightened for one turn. 

The Devil whispers an incantation - Wulgar and Varan feel a twist in their minds as the devil barks, "You two! Fight on my side. I'm an ally." Varan, Wulgar, make a DC 18 Wisdom saving throw or be charmed by the Chain Devil. 

(@Varan; I'll let you choose whether you want to counterspell the Hellish Rebuke or the Charm Person spells.)

The Erinyes reanimates, sending a volley of arrows down over the party. 
Longbow Attack (Varan): 10 Damage: 8 plus 18 poison.
Longbow Attack (Avarice): 15 Damage: 11 plus 16 poison.
Longbow Attack (Ragnar): 13 Damage: 9 plus 12 poison.
Upon a hit, make a DC 14 Constitution saving throw or be poisoned until removed by remove poison / lesser restoration. 

The angelic Avarice ascends into the air, bringing its palms together and separating them as radiant energy gathers in his hands. Two motes burst forth, targeting Keyleth and Avarice. Each of you heal by 15.