(I was just updating the map and realized I made a mistake in the Beasts coordinates. It is in T,U-22,23. So I moved Eiren to T21. Let me know if that is not really where you wanted to be when you look at the map.)

Displacer Beast dex save 15

All of a sudden the displacer beast's legs buckle as the surface he is standing on turns to grease. He falls prone. 

Velmine, Baik, and Corvin are up 

Velmine raises her dagger to throw it at the beast just a second before it falls to the ground, making the ranged attack even harder to hit than it already would be considering her attack at range. Thinking of that, she instead heads directly towards it, stabbing twice, with her shortsword and dagger consecutively.

Attack: 10 Damage: 9 Piercing

Attack: 13 Damage: 4 Piercing

(Separate Sneak Attack roll because one of the two attacks may miss:  19.)

(Both attacks are neutral because prone gives advantage which cancels with the displacement of the beast. If the first attack hits, the second no longer has disadvantage, and so it has advantage. Considering that, here's the advantage roll: 23.)

At the end of her turn, Velmine moves back and away from the beast, until she's at Q22.

Velmine moves to attack the prone beast, but even on the ground Velmine uncharacteristically misses with both dagger. She then retreats out of Melee range using her Fancy Footwork to prevent an opportunity attack. 

Baik and Corvin are up 

Corvin steps forward and smashes his hammer down at the creature.

(Move to S23)

Attack: 24 Damage: 8 + 5 psychic (divine strike)

Baik stays back, and peppers the beast with more Sacred Flames. His spear extended, he smirks as golden light falls atop his foe.

(DC 16 Dex save or 13 Radiant damage.)

Corvin moves forward 5 feet and smashes the prone Displacer Beast with his hammer. (This makes the disadvantage go away until the end of it's turn, not that it really matters since it is just about his turn.)

Baik cast more Sacred Flames down on the beast.

Displacer Beast Dex save 21 (I feel like a prone creature should have disadvantage on dex saves, but I don't see that.)

However the Displacer Beast is about to avoid the holy fires. 

The Displacer beast distressed by the way his feet slipped out from underneath him, stands up. He then moves 10 in the direction of least resistance, south. Ending in T,U-24,25. This provokes an Opportunity attack from Eiren. (Movement is 40 feet. Stand up takes half movement, leaving 20 feet, grease makes the ground different terrain. This leaves him just enough movement to exit the greased ground.)

 Standing on solid ground again he makes two tentacle attacks. The first Tentacle attacks (1,2=Corvin, 3=Xavier) 2 Corvin Attack: 9 Damage: 8 bludgeoning damage + 5 Piercing damage. The first tentacle misses Corvin. The second  Tentacle also attacks (1,2=Corvin, 3=Xavier) 2 Corvin Attack: 14 Damage: 8 bludgeoning damage + 2 Piercing damage. The second attack also misses the cleric, the beast must be tired out.

Eiren has an opportunity attack, Eiren and Xavier are up 

Opportunity Attack: 21 Damage: 14 piercing

(Ooh I think that means its displacement is disabled again, right? Til the end of its next turn, again?)

Eiren curses. "Hey! Watch out for the black stuff on the ground (T,U/22,23). See if you can force it to walk through it again if it does move!" 

He moves to the far side of the grease (V23) and attacks the deadly creature with his rapier once more, seizing the opportunity to attack while it's not phasing.

Attack: 9 Damage: 9 piercing

Attack: 26 Damage: 12 piercing

Eiren is able to hit the Displacer Beast as it moves away from him, causing the displacement field to be disrupted until the end of the beasts "next" round. 

He then shouts a warning to the party about the grease, and then moves around the spot himself and attacks the beast twice. The first attack misses but the second attack is a good solid blow. 

Xavier is up 

Xavier casts frostbite at the beast con 16 save or take 4 cold damage and have disadvantage om next attack

Displacer Beast Dex save 13

The beast takes Xavier's frostbite squarely on one of his tentacles, causing that tentacle to have a disadvantage. (Let me know if I forget to apply the disadvantage.)

Velmine, Baik, and Corvin are up 

Velmine goes quickly past a few members of the party, trying to get close to the Displacer Beast as soon as possible. She finally arrives side-by-side to it while she's on S24. There she makes her two attempts with her sword and dagger to put the creature down once and for all.

Shortsword Attack: 29 Damage: 11 Piercing

Dagger Attack: 14 Damage: 4 Piercing

(+ Sneak Attack: 12)

Velmine moves to attack and deals two good jabs.

(Looks like I forgot to update the map at the top of the round so here it is.)

Baik and Corvin are up 

Corvin  swings his hammer at the beast again.

Attack: 21 Damage: 8 + 3 psychic (divine strike)

Baik, wanting to join In on the action, getting bored of simply showering the Displacer Beast in golden Flames, moves up to D26. From there, he stabs at the Beast with his Spear, as a thunderous boom comes from it when it hits.

Attack: 15 Damage: 17 and 7 If he Moves Booming Blade

Corvin strikes a solid hammer blow and then Baik moves in and delivers the killing spear thrust. 

Everyone receives 140 Xp

(To keep things rolling there is nothing to find at this time. I will be moving the party forward after the post encounter recap. If you really want to do something like take a short rest ect, let me know before you post your next initiative.)

Time in the Doomvault: 0 Days 14 Hours 1 Minute

Baik (25/77) - 0/1 Saving Face, 0/2 rages, 2d6/9d6 healing light, 0/1 tomb of levistus, and 1/2 fourth level spells. Hit Dice 5/8 Warlock, 0/1 Barbarian. 

Corvin (54/66) - 1/4 first level spells, 3/3 second level spell, 1/3 third level spells, 0/3 fourth level spells, 0/1 fifth level spells. 0/5 Embodiment of the Law, 0/2 Channel Divinity. Hit Dice 3/9.

Eiren (46/63) - 1/2 Bladesong, 0/1 Second Wind  0/1 Action Surge, 4/4 first level spells, 1/3 second level spells, 0/1 Blessing of the Raven Queen, 1/1 Arcana Recovery. Arrows 30 remaining (out of 40). Hit Dice: 3/7 Fighter, 2/2 Wizard. 

Velmine (44/57) -Martial Adept 0/1. Bag of Tricks 2/3, Hellish Rebuke 0/1, Darkness 0/1. Hit Dice 3/9 - [Animal Hit Points: [Mastiff: 3/3]

Xavier (42/65) -3/4 first level spells, 2/3 second level spells, 3/3 third level spells. 2/3 fourth level spells. 0/1 fifth level spells. 3/9 Sorcery Points, Healing Hands 0/1, Necrotic Shroud 0/1. Hit Dice 6/9.

Eiren goes over to the White Gate leading to the Forest of Death, while the rest of the party makes a quick search of the area. Finding nothing the party heads towards their next goal, The Golem Laboratories. You are making good time until you turn north and enter a new cavern. Standing by the pool is a Wight and and Dread Warrior (only Eiren can see the Dread Warrior at the start of the encounter as there are trees blocking the rest of the party) The Wight looks refreshed, while the Dread Warrior is kneeling (prone) in front of the pool with cupped undead hands bringing some of the water to his mouth. Both see you, but I'm going to give the Dread Warrior disadvantage on his initiative roll.

Everyone roll initiatives. 

Wright's initiative 4

Dread Warrior's initiative 4

Everyone who rolls a 4 or higher can act.

(Velmine will win against the two of them because of her initiative modifier but for fairness' sake:)

Initiative: 17

Velmine dashes (cunning action) through Xavier's and Eiren's spaces before running directly towards the Wight. On E9, she attacks with her shortsword.

Attack: 29 Damage: 34 Piercing

And then backs off from there until she's at I8.

Corvin initiative: 10

Corvin remains at a distance and fires off a Sacred Flame at the wight.

DC17 dex or 13 damage.