Quote from Secretfool >>

Magron looks at the pool of acid and all the oozes and tentacles. And thinks the best way to stay clear of them is to make sure they can't come to us. Magron flies a bit closer to be right above where the crumbling wall is and touches the stone on the other side which reforms into a slap of stone big enough to close of the pool. (Magron casts Stone shape, how thick would the slab of stone be? He starts with a 5x5x5 cube) 

(Sorry everyone, will post more consistent again) 

 *Three feet.*

"This should keep the oozes and tentacles down there" Magron says.

Maerwyn will use the Crowbar to put extra pressure on the crumbling part of the wall.

"Thanks, Magron. It's a matter of great wonder that these creatures haven't attacked me."

Strength [Crowbar]: 19

The wall starts crumbling even more. Soon, parts of the walls next to it start crumbling.

(wait so the whole room is collapsing? Has a hole be created yet in the wall that crumbled first?) 

Quote from Secretfool >>

(wait so the whole room is collapsing? Has a hole be created yet in the wall that crumbled first?) 

 *Only partially. And there is a small hole.*

Perception 20

Grom hovers over to the opening and tries to look through to the other side.

Quote from ikarbino >>

Perception 19

Grom hovers over to the opening and tries to look through to the other side.

 He can see a few mind flayers and multiple swarms of the glowing rats and a few intellect devourers. In addition, there are three doors at the end of the room. In the center, there is a large pool of brine with the elder brain inside it.

Also, to everyone (except Dusk, because it's telepathy):

It seems like you have finally got near to the end of this tale. And not all stories have a happy ending. But this one will. [More evil laughter]

Maerwyn will use the Crowbar again to put extra pressure on the crumbling part of the wall, but she will be careful with the task so that the wall parts do not harm anyone.

Strength [Crowbar]: 21

Dexterity: Sleight of Hand 20

((Channel Divinity: Destructive Wrath to maximize the damage of Transmuted Spell incendiary cloud changed to deal lightning damage. The elder brain and all within 20 foot radius around it must make a Dex save vs DC 19 or take 80 points of lightning damage. Note: since it isnt clear how large the room is, I of course would center the effect in such a way as to exempt us from it.))

His eyes flashed with divine might as he channeled the wrath of the storm which flowed through his veins and focused his gaze upon the elder brain's tank. "Yes. I think it will." The power poured outwards from him, materializing as a storm cloud center on the tank and in an instant lightning flashed through it to strike at all within.

((Damage is repeated upon anyone who ends their turn in the area or enters into it.))

Dusk floats down with Wispy as he dismisses the hawks. 

He patiently waits, ready to defend himself, as does Wispy, until the opening is big enough to see clearly through.

Both Dusk and Wispy take the Dodge action.

No!!!!!!!!!!!!!!!!! You don't realize what you are doing! Everyone can hear many falling to the ground but they can also hear the sound of physical weapons.

Reaction: Blood Curse of the Souleater: Maerwyn will usher the souls of the fallen creatures to her 'Archfey' patron in exchange for power. She has advantage on weapon attacks until the end of her next turn. She amplifies the curse to regain an expended warlock spell slot.

Free Action: Maerwyn activates 'Blood Maledict' feature.

Bonus Action: Maerwyn activates 'Crimson Rite' feature after taking 7 damage.

Action: Maerwyn will [Tooltip Not Found], Shatter to deal 25 Thunder Damage to the creatures on the other side of the wall within 10 ft radius sphere and each creature must make a Constitution Saving Throw against DC 16. The wall separating them from the creatures should collapse.

Quote from InkedBee >>

Reaction: Blood Curse of the Souleater: Maerwyn will usher the souls of the fallen creatures to her 'Archfey' patron in exchange for power. She has advantage on weapon attacks until the end of her next turn. She amplifies the curse to regain an expended warlock spell slot.

Free Action: Maerwyn activates 'Blood Maledict' feature.

Bonus Action: Maerwyn activates 'Crimson Rite' feature after taking 7 damage.

Action: Maerwyn will cast a spell, Shatter to deal 25 Thunder Damage to the creatures on the other side of the wall within 10 ft radius sphere and each creature must make a Constitution Saving Throw against DC 16. The wall separating them from the creatures should collapse.

 As the wall collapses, everyone near it notices two large groups of illithids, intellect devourers, and glowing rats fighting each other. Many are dead, and some of all three creatures are running away through three doors, which are open. The elder brain is dead.

Magron will ready an attack to hit any of the creature coming within his reach. 

Now able to see into the other chamber, Dusk begins to trace arcane symbols into the air, the trails from his claw leaving a deep violet light. The shadows upon his body thickening and writhing rapidly. His eyes cloud into orbs of blackness.

"Dewch â chyrhaeddiad Evard!" he whispers in an ominous voice.

An area of ground in the chamber beyond darkens as the spell completes and from that darkness erupts shadowy tentacles. These twisting appendages of living darkness grab at the Illithids, the rats and any creature within the spell's area of effect.

Dusk casts Evard's Black Tentacles.

Squirming, ebony tentacles fill a 20-foot square on ground that you can see within range. For the duration, these tentacles turn the ground in the area into difficult terrain.

When a creature enters the affected area for the first time on a turn or starts its turn there, the creature must succeed on a Dexterity saving throw or take 3d6 bludgeoning damage and be restrained by the tentacles until the spell ends. A creature that starts its turn in the area and is already restrained by the tentacles takes 3d6 bludgeoning damage.

A creature restrained by the tentacles can use its action to make a Strength or Dexterity check (its choice) against your spell save DC. On a success, it frees itself.

Dusk will aim to get as many of the Illithids and rats as possible, particularly the ones trying to flee. Creatures that start their turn or enter the area must make Dex Save VS Spell Save DC 19. On Fail targets take 10 bludgeoning damage and become restrained. Creatures already restrained by the tentacles take the 3d6 damage automatically at start of turn.

Dusk's eyes and shadows return to normal upon completion of the casting. "That might hold them a little bit." He says with a shrug. He scratches his chin as he leans on his staff. He acts entirely nonchalant about calling forth an aspect of a cosmic horror.

Quote from Cyb3rM1nd >>

Now able to see into the other chamber, Dusk begins to trace arcane symbols into the air, the trails from his claw leaving a deep violet light. The shadows upon his body thickening and writhing rapidly. His eyes cloud into orbs of blackness.

"Dewch â chyrhaeddiad Evard!" he whispers in an ominous voice.

An area of ground in the chamber beyond darkens as the spell completes and from that darkness erupts shadowy tentacles. These twisting appendages of living darkness grab at the Illithids, the rats and any creature within the spell's area of effect.

Dusk casts Evard's Black Tentacles.

Squirming, ebony tentacles fill a 20-foot square on ground that you can see within range. For the duration, these tentacles turn the ground in the area into difficult terrain.

When a creature enters the affected area for the first time on a turn or starts its turn there, the creature must succeed on a Dexterity saving throw or take 3d6 bludgeoning damage and be restrained by the tentacles until the spell ends. A creature that starts its turn in the area and is already restrained by the tentacles takes 3d6 bludgeoning damage.

A creature restrained by the tentacles can use its action to make a Strength or Dexterity check (its choice) against your spell save DC. On a success, it frees itself.

 

Dusk will aim to get as many of the Illithids and rats as possible, particularly the ones trying to flee. Creatures that start their turn or enter the area must make Dex Save VS Spell Save DC 19. On Fail targets take 10 bludgeoning damage and become restrained. Creatures already restrained by the tentacles take the 3d6 damage automatically at start of turn.

Dusk's eyes and shadows return to normal upon completion of the casting. "That might hold them a little bit." He says with a shrug. He scratches his chin as he leans on his staff. He acts entirely nonchalant about calling forth an aspect of a cosmic horror.

 Most of them get restrained, although a few manage to dodge the tentacles.

Maerwyn will attempt to aim her Crossbow at the Mind Flayers who manage to dodge the tentacles. She will attack twice releasing the glowing bolts that have been infused with Crimson Rite magic.

Attack

Crossbow [Light]: Attack: 26 Damage: 7 + 3

Attack: 14 Damage: 5 + 5

Quote from InkedBee >>

Maerwyn will attempt to aim her Crossbow at the Mind Flayers who manage to dodge the tentacles. She will attack twice releasing the glowing bolts that have been infused with Crimson Rite magic.

Attack

Crossbow [Light]: Attack: 26 Damage: 5 + 2

Attack: 11 Damage: 10 + 1

 Sanguine Mastery: Rerolling Hemocraft Die for 1st Attack: 2 Thunder Damage.