Katarina notices that she isn't in the best position to be tearing her enemies to pieces... and that makes her angry.

Bonus action: RAGE!!!
Wild Surge: 1
Shadowy tendrils lash out at Katarina's enemies, who must each make a DC 16 Con save or take 8 necrotic damage. Katarina also gains 2 temp hp.

Movement: Katarina goes full kitty-parkour to scale the walls to climb the walls and get into melee with the wights (specifically, the blue wight). Athletics to pull it off: 20 (advantage from RAGE). At the end of her movement she'll be in the upper-right corner of the chamber, right behind the blue wight.

Action: Katarina hisses and attacks the blue wight recklessly, using her crystal longsword in both hands for maximum damage
Longsword (two-handed) - Attack: 19; Damage: 8 (magical slashing) + 3 (radiant)
Longsword (two-handed) - Attack: 25; Damage: 9 (magical slashing) + 5 (radiant)

Attacks against Katarina have advantage until her next turn. Also, her AC is 16 for right now until she has the chance to get her shield out.

Marching order: Davis :: Vanizi :: Celeste :: Zylynne :: Vesta :: Katarina

Davis and Vanizi lead the party down steep stone steps, at least 30 feet underground, into a large, 30'x30' chamber. Part of the west wall has collapsed, creating an opening into another chamber. Hidden around the chamber are five pale, desiccated warriors wearing wicked-looking armor, who spring out and attack as soon as Vanizi and Davis reach the bottom of the steps! (updated map)

Round 1:
Katarina rages and shadow-whips the wights! (DC16 Con: Pink(9) :: Black(7) :: Red(11) :: Green(9) :: Blue(7)) but the necrotic energy of her wild magic is less effective on these undead beings. She then uses her ACTION to climb over and around the wights to flank behind the blue wight (At the DM’s option, climbing a slippery vertical surface or one with few handholds requires a successful Strength (Athletics) check. You just made the DC20 check! I will save your attack rolls for next round.)
Vanizi ??
Wights

• Pink makes a longsword attack (Attack: 12 Slashing Damage: 10) and also reaches out to touch Davis and attempt to drain some of his life force (Attack: 17 Damage: 5 - if this hits, make a DC 13 Constitution saving throw or your hit point maximum is reduced by the amount of damage taken.)
• Black also attacks Davis! (Longsword Attack: 8 Slashing Damage: 9)  (Life Drain Attack: 12 Damage: 4 - if this hits, make a DC 13 Constitution saving throw or your hit point maximum is reduced by the amount of damage taken.)
• Red finishes the trinity of attackers against the paladin. (Longsword Attack: 9 Slashing Damage: 8)  (Life Drain Attack: 22 Damage: 6 - if this hits, make a DC 13 Constitution saving throw or your hit point maximum is reduced by the amount of damage taken.)
• Green attacks Vanizi. (Longsword Attack: 8 Slashing Damage: 7)  (Life Drain Attack: 14 Damage: 8 - if this hits, make a DC 13 Constitution saving throw or your hit point maximum is reduced by the amount of damage taken.)
• Blue also attacks Vanizi. (Longsword Attack: 11 Slashing Damage: 8)  (Life Drain Attack: 6 Damage: 5 - if this hits, make a DC 13 Constitution saving throw or your hit point maximum is reduced by the amount of damage taken.)

Davis
Celeste
Zylynne
Vesta

Vanizi will cast Hex on the wight (Blue) to her left. She then draws her greatsword as she casts Green-Flame Blade and attacks the same wight (Blue). 
(Greatsword Attack: 13, Damage: 9 slashing + 5 fire + 5 necrotic)  

If the attack hits, the green-flame jumps from the sword to the wight (Green) in front of her. (13 fire damage) 

[Davis saves from the Red wights life drain. I assume this is a magical attack for the sake of heavy weapon mastery.]

Davis will attack the Pink Wight, moving to Black when Pink falls.

attack 1 Holy Avenger Longsword: 26 slash: 12 + radiant: 8

attack 2 Holy Avenger Longsword: 16 slash: 11 + radiant: 6

He will then move into the room, taking the OA from pink if it is still standing, to open some space for others to attack.

"AHHH! OUTTA THE WAY!!!" Zyl screeches as she sees the wights engage the party, and once the path is cleared, she steps down toward the horrifying creatures, suddenly growing several times over, and her axe begins to glow like fire. There is now a giant flame-axe wielding fairy in the midst of the wights.

Movement: moved 5ft into melee with the wights

Bonus Action: RAGE (Elemental Cleaver: fire)

Action: Attacking Red Wight (with advantage to flanking with Davis)

Attack 1: 22 to hit, 16+3 (from rage) +3 (Elemental Cleaver) for 22 fire damage

Attack 2: 23 to hit, 13 +3 (from rage) +2 (Elemental Cleaver) for 18 fire damage

Vesta will stay where she is, at the back of the party. Three streaks of fire erupt from her free hand toward three of the wights.

Scorching Ray

Against Blue - Attack: 31 Damage: 2

Against Green - Attack: 27 Damage: 7

Against Black - Attack: 27 Damage: 9

(Or whichever ones are left standing!)

She will also use her Elemental Affinity to Fire to add 5 damage to that first damage roll against Blue.

Round 1 (con't):
Katarina rages and shadow-whips the wights! (DC16 Con: Pink(9) :: Black(7) :: Red(11) :: Green(9) :: Blue(7)) but the necrotic energy of her wild magic is less effective on these undead beings. She then uses her ACTION to climb over and around the wights to flank behind the blue wight.
Vanizi hexes the blue wight, but her attack is deflected by the creature's studded leather armor.
Wights

• Pink makes a longsword attack (Attack: 12 miss) and also reaches out to touch Davis and attempt to drain some of his life force (Attack: 17 miss)
• Black also attacks Davis! (Longsword Attack: 8 miss)  (Life Drain Attack: 12 miss)
• Red finishes the trinity of attackers against the paladin. (Longsword Attack: 9 miss)  (Life Drain Attack: 22 Damage: 6)
• Green attacks Vanizi. (Longsword Attack: 8 miss)  (Life Drain Attack: 14 miss)
• Blue also attacks Vanizi. (Longsword Attack: 11 miss)  (Life Drain Attack: 6 miss)

Davis (Life Drain is not a magic attack, so no advantage on saves against it. Good news is you still made it!) hits the pink wight twice with his holy longsword, but it stays on its feet! As he moves through the line of wights, the pink one takes an opportunity to swing once more at the paladin! (Attack: 10 Damage: 6)
Celeste ???
Zylynne comes screaming in, growing into a giant, flame-axe wielding fairy! She attacks the red wight in front of her, hitting twice with her flaming axe. The damage is massive, but the wight remains on its feet... 
Vesta unleashes bolts of fire against three separate wights, hitting all but barely singeing them.

Round 2:
Katarina
Vanizi
Wights

Quote from Rhanloi >>

Davis (Life Drain is not a magic attack, so no advantage on saves against it. Good news is you still made it!) 

 I was referring more to this part for the magical attack. thanks!

• While you are wearing heavy armor, bludgeoning, piercing, and slashing damage that you take from nonmagical attacks is reduced by 3.

Vanizi again casts Green-Flame Blade and swings her greatsword at the wight (Blue) to her left. 
(Greatsword Attack: 13, Damage; 9 slashing + 7 fire) 

If the blow hits, she causes the green flame to jump to the next wight (Green) to her right. (Damage: 7 fire) 

 (Sorry for the delay! Been crazy with preparing for cruise ships to visit the community tomorrow.)

Celeste really wanted to look in those tombs back there but she preferred to stick with the group. After 'rubber necking' on her way down in hopes of catching a peak, which wouldn't be possible, her attention is eventually brought forward to the group. "You guys made some new friends!" She chimes in jest. The druid licks her finger and holds it up into the air. Her face looks thoughtful, as if calculating a few things. Inhaling a breath, she gives it a go. "Swoosh!" She gestures with her arms. "Boop!"

Katarina is just going to go ahead and unleash her two attacks from the previous post against the blue wight.

Action: Katarina hisses and attacks the blue wight recklessly, using her crystal longsword in both hands for maximum damage
Longsword (two-handed) - Attack: 19; Damage: 8 (magical slashing) + 3 (radiant)
Longsword (two-handed) - Attack: 25; Damage: 9 (magical slashing) + 5 (radiant)

Round 1(con't):
Celeste follows Davis' movement with a wall of water, crashing down on the three wights (DC19 Dex saves: Black(15), Red(4), Green(19)) She then launches a luminous arrow at the green wight.

Round 2:
Katarina...
Vanizi swings again - and misses again!
Wights

Round 2 (con't):
Katarina...
Vanizi swings again - and misses again!
Wights

• Pink makes a longsword attack against the giant fairy (Attack: 11 Slashing Damage: 3) and also reaches out to touch Zyl to drain some of her life force (Attack: 24 Necrotic Damage: 7)
• Black stands up and makes a soggy attack on Zyl! (Longsword Attack: 5 Slashing Damage: 6) (Life Drain Attack: 8 Necrotic Damage: 4)
• Red stands and turns to attack Davis. (Longsword Attack: 18 Slashing Damage: 4) (Life Drain Attack: 11 Necrotic Damage: 6)
• Green gets up from the giant puddle and attacks Vanizi again. (Longsword Attack: 21 Slashing Damage: 5) (Life Drain Attack: 5 Necrotic Damage: 8)
• Blue turns to attack the wall-crawling tabaxi, Katarina. (Longsword Attack: 22 Slashing Damage: 7) (Life Drain Attack: 19 Necrotic Damage: 4)
• On any successful Life Drain attack, make a DC 13 Constitution saving throw or your hit point maximum is reduced by an amount equal to the damage taken.

Davis 
Celeste 
Zylynne  
Vesta

Quote from Mister_Whisker >>

Katarina is just going to go ahead and unleash her two attacks from the previous post against the blue wight.

Action: Katarina hisses and attacks the blue wight recklessly, using her crystal longsword in both hands for maximum damage
Longsword (two-handed) - Attack: 19; Damage: 8 (magical slashing) + 3 (radiant)
Longsword (two-handed) - Attack: 25; Damage: 9 (magical slashing) + 5 (radiant)

Also, nat 1 on the con save, but if she is in Davis' Aura of Protection she should get a +5 bonus which would still bring that up to 14 (nat 1 isn't an auto-fail except on article rolls and death saves).

She was attacking recklessly, so the wight technically should have had advantage when it was swinging away at her. I'm not sure if she could have grabbed her shield after two-handing her longsword to bring her AC back up to 18 or not.

Davis will attack Red, once they fall, move to black, then to green.

attack 1Holy Avenger Longsword: 27 slash: 14 + radiant: 6

attack 2 Holy Avenger Longsword: 19 slash: 14 + radiant: 6

Zyl manages to dodge and smack most of the incoming attacks away from her, but screeches again as the necrotic energy leeches into her from the pink wight. "OWWW!!!" She'll then take her swings back at the pink wight. "Don't get your disgusting goopy hands on me!"

Action: Attack (normal)

Attack 1: 17 to hit, 12+3 (rage) +1 (elemental) , 16 fire damage

Attack 2: 22 to hit, 7+3(rage) +3 (elemental) , 13 fire damage

Bonus Action:

Mighty Impel: Zyl reaches for the black wight and attempts to pick it up and hurl it 30ft across the room! (Strength save, DC 16, and she will try to make him hit the ceiling and fall to the ground prone as well)

(Oh yeah - thanks for the reminder, Whisker! And equipping the shield would be an action, so not yet!)

Round 2 (con't):
Katarina hits the blue zombie twice in a reckless attack!
Vanizi swings again - and misses again!
Wights

• Pink makes a longsword attack against the giant fairy (Attack: 14 Slashing Damage: 7) and also reaches out to touch Zyl to drain some of her life force (Attack: 24 Necrotic Damage: 11)
• Black stands up and makes a soggy attack on Zyl! (Longsword Attack: 5 Slashing Damage: 9) (Life Drain Attack: 12 Necrotic Damage: 6)
• Red stands and turns to attack Davis. (Longsword Attack: 7 Slashing Damage: 6) (Life Drain Attack: 18 Necrotic Damage: 5)
• Green gets up from the giant puddle and attacks Vanizi again. (Longsword Attack: 24 Slashing Damage: 15) (Life Drain Attack: 11 Necrotic Damage: 7)
• Blue turns to attack the wall-crawling tabaxi, Katarina. (Longsword Attack: 17 -Adv 13 Slashing Damage: 3) (Life Drain Attack: 19 -Adv 20 Necrotic Damage: 6)
• On any successful Life Drain attack, make a DC 13 Constitution saving throw or your hit point maximum is reduced by an amount equal to the damage taken.

Davis attacks the severely injured red wight, dropping it to the ground. The paladin turns his attention to the black one and lands another solid blow! 
Celeste ...
Zylynne  feels the necrotic damage from the undead touch, and uses her magic greataxe to return the pain! She nearly slices the monster in half. The giant fairy rage-machine then picks up the black wight and tosses it across the room!! (DC16 Str: 13 - Sorry - it's just a toss to another part of the chamber. Now if there was a bridge, or chasm... =)
Vesta ...

Katarina uses her reaction to activate the Unstable Backlash feature, allowing her to roll again on the Wild Surge table, getting a 4:

"Magic infuses one weapon of your choice that you are holding. Until your rage ends, the weapon’s damage type changes to force, and it gains the light and thrown properties, with a normal range of 20 feet and a long range of 60 feet. If the weapon leaves your hand, the weapon reappears in your hand at the end of the current turn."

Katarina will infuse her longsword, giving it the light and thrown properties as well as converting its damage type to Force (not that I think it matters much against the wights one way or another, but I guess she can dual-wield it with one of her handaxes until the next time something hits her).

With the flurry of attacks coming and going, Celeste takes a bit longer than usually necessary to act. After a few moments of analyzing the battlefield and finding her opening, she draws back her celestial bow, firing off two bolts in succession. One tinged blue with frost targets green while her luminous arrow soars to the back towards black.

Cast: Frostbite Con save DC19 or take 7 cold damage and have DA on next attack
BA: Luminous arrow Attack: 19 Damage: 18