Into the Mists-The Condemnation of Strahd

Ban recoils as the creature flings muck about, and she quickly unsheathes one of her least favorite daggers and steadies aim from above. A flash of steel is all that's seen of the dagger that was in her hand as she throws it at the creature. She pulls out another dagger and kneels down to minimize like of sight.

Sneak attack :11

Attack: 8 Damage: 8

Initiative: 11

Bonus Action: Stealth: 24

Initiative Order:
Gillain: 18
Shambling Mound: 18
Gimble: 15
Farris: 10
Ban: 9
Tio: 7
Bob: 6

Gillain touches her holy symbol and for a moment a shimmering light bubble seems to encircle her. Gillain thrusts with her spear. She is sure the strike will miss but at the last moment, the creature moves in a way that Gillain's spear strike is true and the blade sinks into the creature. 

The Shambling Mound, once attacked, turns its attention towards Gillain. It lashes out with its 2 great fists of debris at the Paladin.
Strike #1: 23
Strike #2: 14
Both attacks miss.

Gimble utters the arcane words and 4 missiles of magical energy speed from his hand and strikes the monster. Bits of debris pop off as the missiles strike.

Farris fires a crossbow bolt. The bolt streaks across the room, glowing with some radiant energy and strikes the creature. Again bits of debris fly off where the bolt strikes.

Ban launches her dagger at the creature. It flies forward, striking the Shambling Mound. The dagger embeds itself into the creature.

Tio's arms and hands glow for a moment and a shell of translucent energy covers them, then expands. Tio throws a punch at the air in front of her and the energy surrounding her arm stretches out, taking the appearance of a punching fist, striking the Shambling Mound. Small bits of debris flies from the creature.

Bob points his hand at the creature. An eerie green glow dances across Bob's outstretched hand and flies towards the creature. As the green energy goes forward it takes the shape of an eerie green glowing skeletal hand. The hand grabs the creature and flashes out of existence. Pieces of the creature fall off where the hand grabbed it. 

DM: Everyone's 1st attack hit and did some damage.
Post for Round 2

Gillain ducks one way, then the other, and the shambling mound misses, but she gets the impression that if it had connected it would have been bad news!

She looks sideways to Tio, with her power arms, and nods. Then she swings at the monster again... once... and twice... with her spear.

Attack action (spear): Attack: 17 Damage: 9 (piercing damage)

Bonus action (polearm master): Attack: 12 Damage: 6 (bludgeoning damage) 

Gimble:

Continuing to move so he is well out of the reach of this creature, Gimble shoots more magic missiles across the room at it, using his last powerful spell to aid the others in taking it down:

Magic Missile at level 2:  16

Bob wades into the water behind the shambling creature and calls on the infinite network of fungal spores inhabiting his body and his shillelagh.

Bob uses his action to expend a usage of Wild Shape and use Symbiotic Entity.

Ban pulls another dagger out and looks for an opportunity where the creature is particularly open. Picking the right moment, the eladrin short hops and throws both daggers in a cross armed motion. As she lands, she kneels to limit visibility.

Sneak attack :10

Attack: 19 Damage: 7

Bonus Attack: 8 Damage: 1

Round 2:
Gillain: 18
Shambling Mound: 18
Gimble: 15
Farris: 10
Ban: 9
Tio: 7
Bob: 6

Gillain thrusts her spear towards the creature. The twigs, branches, sludge, and debris collide and push aside the spear thrust. Gillain spins and tries to strike the creature with the shaft end of her spear but, misses again.

The Shambling Mound makes 2 attacks against Gillain.
Strike #1: 12
Strike #2: 18
The creature strikes at Gillain twice, missing both times.

4 bolts of magical force fly from Gimble's outstretched hand, striking the creature. A large chunk of debris falls from the creature in front of Gillain.

Farris loads and fires another crossbow bolt. The glowing bolt streaks across the room, striking the creature. Another large chunk of debris falls from the creature.
DM: roll for the crit damage for this attack, please.

Ban does a short hop and throws 2 daggers at the creature, 1 strikes the creature while the other goes wide, hitting the wall on the opposite side of the room. 

Tio will continue attacking with Gillain this time throwing two strikes one as her action and the other as a bonus action.

Attack1: 22 Damage: 4

Attack2: 16 Damage: 4

Gimble:

Out of his powerful spells, Gimble stays away from the monster and tries to freeze it enough to slow down its attacks (give it disadvantage on its next attack).

Frostbite:  DC 13, Frost damage:  6

Gillain looks quickly left and right and sees her companions scoring punishing hits on this hulking monster. For now she is happy to monopolise it’s attention, whilst sizing each other up and trading misses; like two prize fighters who know that even a single big-hit, landed, might be the knockout blow either way.

Seeing chunks of this thing fly off, Gillain redoubles her efforts as she realises it can be hurt, and that maybe her band of friends can emerge victorious!

Attack action (spear): Attack: 18 Damage: 8 (piercing damage)

Bonus attack (polearm master): Attack: 12 Damage: 8 (bludgeoning damage) 

Bob sets the cloud of spores surrounding him on the shambling creature since it did little to move away from the microscopic fungi.

Using reaction to use Halo of Spores: 6 necrotic damage

He then swings his shillelagh at the craggy creature.

Attack: 8 Damage: 12

Symbiotic Entity bonus necrotic damage on hit: 3

Growing concerned she'll run out of daggers she's willing to sacrifice to the fetid area below, Ban selects a random dagger off a belt sheath and carefully draws aim. Breathing in time, the eladrin throws a dagger at the creature and retrieves another from her opposite side.

Sneak attack :2

Attack: 26 Damage: 9

DM: OK, unless I missed it, Tio's post was for Round 2. It seems everyone went ahead and posted actions for round 3.

Round 2:
Tio, using her Astral Arms, strikes at the creature twice. Both of Tio's strikes miss the creature.
Round 3:
Gillain: 18
Shambling Mound: 18
Gimble: 15
Farris: 10
Ban: 9
Tio: 7
Bob: 6

Gillan strikes at the creature again with her spear. Gillain pierces the creature with her spear tip, doing damage but, misses with her second attack. 

The Creature again strikes at Gillain twice:
Strike #1: 22
Strike #2: 19
Gillain easily dodges the creature's attacks.

Gimble casts his spell. Frost begins to form on the wood and debris that make up the body of the creature.
Con roll: 14
A thick layer of frost forms over the creature's body. As the creature moves parts of its frozen body crack and falls to the ground.

Farris loads and fires another crossbow bolt from his Heavy Crossbow. The bolt glows as it streaks forth, striking the torso of the creature and tearing through it. 

As the bolt flies through the Shambling Mound, a trail of green energy encompasses the bolt and trails out of the creature's body. The trail of green energy only lasts for a moment and seems to dissipate into nothing. The emerald light of the creature's eyes, not really noticed until this moment,  flair, then fade and the eyes are dull and grey now. The form of the creature bubbles and with a loud pop crumbles into the water. 

There is silence for a moment then the apparitions start wailing. The scream of "NNNNOOOO!" comes from their mouths in unison and they fade from view.

There is a second moment of silence. All the party sees is each other standing on this battlefield, hearing each other breathe.

Suddenly the whole place starts to fumble and shake. Large pieces of the ceiling start to fall into the cavern where the party is standing. 
Actions?

Gillain looks desperately around the room as it collapses in on itself. She raises her shield over her head as best she can to ward off the falling debris. “What happened? The place is collapsing!!... I think we’ve got to get out!... Oh gods!....”. She moves over towards the secret doorway they came through, and waits to usher everyone else out, making sure they’re all through the doorway and safe before following behind...

Gimble:

Just as his focus was directed at the dying creature to see if it housed any magical trinkets within its debris, the ceiling started falling down on them!  Already fairly close to the secret door after having backed away from fearsome creature, Gimble scoots out the door to at least get out of the crumbling section of the main room, continuing to run if more than just the one room is collapsing.

Bob goes from whooping in triumph to hollering in fright in mere moments after felling the strange beast-structure. "Och! I know a bit about stone an' I'd say, based on how it's fallin' an' everythin', that we should RUN FER OUR LIVES!"

Not wasting any more time he transforms into a wolf using his Wild Shape ability, moving almost twice as fast as he would as a stumpy-legged dwarf as he sprints after the others.

Gimble sees no magical trinkets in the debris as it melts into the water.

The house starts to shift and shake with parts of the ceiling falling to the ground. As the party races forward the area is flooded with the sounds and smells of a house falling in upon itself.
https://www.youtube.com/watch?v=63hwhanrrXw

The party makes its way to the staircase that led them down to this hidden lair. As they make their way up the stairs, the walls around them start to crumble. Dust rises from the crumbling walls making it hard to see and breathe. The very floor seems to pitch and roll with each step the party takes, making it difficult to maintain footing. 

DM: Everyone please roll 3 Dex Rolls for the ensuing escape and 1 Con roll.
The Dex Rolls are at a DC of 10 to keep from stumbling (1 for each floor the party must traverse to get to the main entrance) and the Con Roll is a DC 10 as well, so the characters do not start choking.
Once rolled I will continue the narrative to the exit.