Ven is running full on in the west room, nothing could be worse than this specter.
WIS save vs frightened (using my inspiration point) : 15

Kandalou will make a beeline as far away of the ghost as possible, "ZOINKS!" he yells.

DC 15 Wisdom Save: 10 (memory drain, as you type it, applies to ability checks and attack rolls, what about save rolls? If so, -4)

((LOL I ROLLED A 1!!))

Kalak reacts first. The wizard launches a different kind of magical sparks from his fingers, and his aim is impeccable. All six sparks hit the ghost's torso. (Apparition takes 26 force damage.)

Shai moves closer to the enemy {BR-20}, and lets her magical fits engage the phantom. (Apparition takes 11 magical bludgeoning damage.)

Being her cautious self, the monk then assumes a defensive stance.

DM's Screen:

Quadere evokes Oghma's light and lets her entire body bask in it. The apparition reacts and seems to shrink in pain a bit, but doesn't feel particularly enticed to float away.

Someone else does run away, though. Kandalou cannot resist the fearsome apparition's form. Their tattered but once fancy robes reveal a bit too much of the underlying gory scenes. The fighter makes it all the way to the oval room {BS-34}, and is now just a few feet away from the gigantic (but immobile) central marble statue.

Ven too decides to dash away. He reaches the west wall first, then continues toward the bottom southwest corner of the room. Now fully inside the room, the bard notices that the floor of this chamber is lined with small depressions at regular intervals, and that water rapidly and continuously drips from the ceiling into the center of each depression. Strangely, this helps Ven calm down a bit, and whatever magical fear the apparition forced into his being is now gone!

Vishnu waits for her opportunity and then releases an arrow. Its magical coating is enough to harm the ghost, and significantly at that. (Apparition takes 27 magical piercing damage.)

(Apparition goes next.)

The apparition turns to face Shai and moves though her body. The monk can feel the ghost come out the other side, but she is so close to the wall that it can only mean the ethereal being is now within the rock. (This would trigger opportunity attacks for Quadere and Shai, but they would be able to hit nothing but either Shai herself or the wall.)

A few seconds later in the oval room, Kandalou sees the huge statue start moving once again. It doesn't attack the fighter just yet, but it moves to block the passage into the tunnel leading west.

END OF INITIATIVE ROUND 1

FRIGHTENING APPARITION - INITIATIVE ROUND 2

• 19. Kalak (38/38) - source of Light;
• 14. Shai (66/66) - dodge;
• 13. Quadere (66/66) - source of Light;
• 13. Kandalou (48/94) - frightened, memory-drained (d4 penalty to ability checks and attacks);
• 09. Ven (56/57) -  
• 08. Vishnu (66/66) - 
• 00. Apparition/Marble Statue -  

MAP:

 

NOTES: ...

(Everyone can take their turns. Kandalou is still constrained by the details in the spoiler within this post.)

Feeling somewhat shaken by the feeling of the ethereal being just passing straight through her, Shai decides that staying at range is the safest option and moves east along the passageway to where the outcrop of rock (~BP26) pulling her crossbow from her shoulder and readying a bolt in place as she advances and then kneels to steady herself and takes a shot at the statue.

Crossbow Attack: 12 Damage: 6

and then will finish her movement by wedging herself against the North wall to hopefully give her some cover.

Vishnu blinks rapidly.

"How . . .nope, just shooting."

Attack: 26 Damage: 7 magical piercing

Sneak Attack: 23

Kalak detonates a fireball behind the now-moving statue (Centered on BP-38)0

Dex save [DC16], success is half damage

Potential damage: 16

(Wow...)

Kandalou brushes the sweat off of his forehead, "Finally away from that... THING," he mutters to himself. It is at this point that Kandalou notices the statue move to block the doorway... that his friends are... away from him. "Oh... well... damn," he mutters.

DC 15 Wisdom Save: 19 - 3

((Finally! I can actually do my next turn!))

DM's Screen:

Kalak sends a fireball through the statue's legs, which detonates a safe distance away from his fighter companion. The statue is enveloped in the flames, but seems little bothered by it. (Marble Statue takes 8 fire damage.)

Shai finds a protective nook in the tunnel's walls and shoots her crossbow. Unfortunately, the bolt's trajectory is a bit off. It whizzes by its target and hits the wall on the other side of the room. 

(@Drache: Oof... what a horrible damage roll! Sorry, buddy.)

In his fear, Kandalou can't know exactly where the apparition went, so he stays put. The moment of relative calm pays off and the fighter regains control of his wits (no longer frightened).

Vishnu seems a bit unsure/surprised(?) at first, but decides to shoot an arrow at the statue anyway. Her bow infuses some magic onto the projectile, which flies true and opens a crack on the marble! (Marble Statue takes 30 magical piercing damage.)

(@Superbad: There is no need to roll the d4 penalty on saving throws.)

(OOC: Let's give a bit of extra time for Quadere and Ven to take their turns. Also, in case it wasn't clear, Ven is no longer frightened either.)

Ven finds himself in a strange room and gathers his wits. "There is nothing to be afraid, Ven..." he keeps repeating to himself.
He rushes back and passes his companions (Dashing to BR24)

Ven sees Kandalou in a dire situation, in front of the huge marble statue and shouts:
“Do you see over yonder, friend, one hulking giant? I intend to do battle with it and slay it.”
Bonus action: Bardic inspiration for @Kandalou

Bardic inspiration (1d8):
You can roll the die and add the number rolled to one ability check, attack roll, or saving throw it makes.
You can roll that die and add the number rolled to a weapon damage roll you just made.
Alternatively, when an attack roll is made against you, you can use your reaction to roll the Bardic Inspiration die and add the number rolled to your AC against that attack, after seeing the roll but before knowing whether it hits or misses.

Quadere looks at the now animated statue for a moment. Seemingly reaching a conclusion, she moves forward to BQ-21 and attempts to test it's defenses with a brief flash of light (DC16 Dex Saving Throw or take 9 Radiant damage). Regardless of the result, she then tucks herself in behind the wall at BP-21 and watches carefully from around the corner.

DM's Screen:

Noticing the fire isn't perhaps the best weapon to use, Quadere tests out some of her holy power. Curiously, the holy flames cause the damage the arcane fire couldn't. (Marble Statue takes 16 radiant damage.)

Meanwhile, Ven traverses back through the room he had entered. As he moves, he notices manacled chains bound to the floor which are mounted near many of the depressions. He continues on, notices the danger his fighter friend might be in, and delivers an inspirational quote of his own making (Kandalou has a Bardic/Combat Inspiration d8.)

THE MANACLES:

(Marble Statue goes next.)

The statue brings its two hands down on Kandalou, as the ceiling slowly moves down.

-> Slam vs. Kandalou: Attack: 11 Damage: 58 bludgeoning.

-> Slam vs. Kandalou: Attack: 14 Damage: 50 bludgeoning.

Both of the heavy hands slam on the ground creating small craters. Kandalou steps aside in both occasions, counting himself lucky.

END OF INITIATIVE ROUND 2

FRIGHTENING APPARITION - INITIATIVE ROUND 3

• 19. Kalak (38/38) - source of Light;
• 14. Shai (66/66) - 
• 13. Quadere (66/66) - source of Light;
• 13. Kandalou (48/94) - memory-drained (d4 penalty to ability checks and attacks), Bardic/Combat Inspiration (d8);
• 09. Ven (56/57) -  
• 08. Vishnu (66/66) - 
• 00. Apparition/Marble Statue -  

MAP:

 

NOTES: ...

(Everyone can take their turns.)

Vishnu’s eyes widen as she witnesses the statue’s destructive power.

"That . . .could be a problem."

She looses another arrow at it.

(On the offchance she can hide: 20)

Attack: 23(Adv: 25) Damage: 9 magical piercing

Sneak Attack: 21

Quadere's eyes narrow as she sees the creature's raw strength and large size. "We can't afford to take any hits like that! Everybody stay away from the statue, and be ready if that apparition comes back!" Then she sends another gout of holy fire (DC16 Dex Saving Throw or take 12 radiant damage) at the statue, hoping to distract it briefly.