Quote from Engineered_Beard >>

Progo initiative: 4

Position: column 7

Row: 4

 Well that's in the wall on the corner so how about F5 for Progo 

Initiative : 6
Position A8 (rolled 1 and 8)

Tharanau throws stones and hands full of dust at everything around him. When they reach the barrels, he does the same.

He is so shocked to finally encounter the enemy, that this rolling barrel takes away his composure and he needs just a moment to collect himself and get ready to attack.

initiative: 6 (on char sheet)

position: C4

[I don't think we're supposed to roll positions, just say where we want to be, no?]

second initiative roll, Roll-Off against Seth and the mimic who both had an initial initiative of 6: this time: 10

Initiative is as follows. Draw were resulted by a higher Dex score.

1.Tharanau

2. Mimic

3. Goraseth

4. Tryncaryn

5. Progo

I will post map when I will be able, but we can proceed when Tiomila is ready to act.

Tharanau realises that all his allies are frozen when this beast comes to view. And even the beast itself takes a surprised second to understand what is happening. 
So Tharanau takes a stand, moves his hands and sends lightning towards the monster.

ranged attack roll for witch bolt: 18, for damage 7

He shouts to his companions: "Remember, don't let it touch you!!"

A beam of crackling, blue energy lances out toward a mimic, forming a sustained arc of lightning between Tharanau and the mimic. Mimic gets hit as it starts to roll, and the hit makes it jump a little out of electrification.
(Attack lands, and mimic gets 7 points of lighting damage)

Mimic gets a little dazzled, rolls and starts attacking first thing it sees, it happens to be Progo. 16 to hit with its Pseudopod attack. Mimic Lashes sticky  tongue at Progo dealing 8 bludgeoning damage. The tongue sticks to Progo's body, and Progo is now grappled. (DC 13 to escape and check made with disadvantage /unless you get something to get advantage then it would make it straight roll/) 

Goraseth is surprised by this living-barrel but when he sees his camarade stuck, he jumps into action. Rushing 10ft from the monster he unleashes his dragonborn breath. Ice crystals form and cover the montruous barrel. He then quickly holds his amulet "Bahamut, protect me". A shiny silver magical barrier appears suddently around him. Feeling empowered by his god, he shouts at the monster: "Come here ugly face, pick up someone your size !"

Action = Breath Cold damage: DC11 Con or 3 cold damage (1/2 reduced)
Bonus action = casting Shield of faith of himself (now AC 21)

Tryn‘s eyes bulge as he sees the monster move and lick at Progo. In a snap reaction, he hurries ten feet forward (to E4) and assists Progo to escape the monster’s grapple (help action), before stepping a few feet back (to E2). 

(Since Progo is grappled, is he in the breath attack too?)

Goraseth could easily aim the breath cone to not include Progo.

( Progo has a -1 STR modifier so he wasn't going to bother trying to break free, but can't waste a helping hand!) 

Despite being wary of objects that could turn out to be this mysterious mimic, Progo was getting to the point of assuming they wouldn't find it this way, resorting to poking things with the tip of his raiper. He never saw the eye open and didn't realize the barrel was moving of its own accord until it had him in its grasp. Progo hadn't got to be the best Progo he coukd be by being the strongest, but by being the pokiest! As he tried to wriggle is arm into place to make a strike, he feels the pull on his shirt behind him and desides that may be enough to try and break free.

Strength saving throw: 0

Failing to break free he shouts back to the others in a strained, breathless voice, "have no worries, Progo has it right where Progo wants it. Feel free to give it the killing blow!"

Tharanau keeps concentrating on sustaining the blue lightning arc that still connects him to the monster and deals another shock to the creature (Lightning damage 11), hoping to free Progo by killing the thing. 
"Keep at it!" He shouts to his companions. 

Mimic feels his prey is trying to escape his tongue grip, so it tightens up and reels Progo Closer to Bite him (21 attack roll) His mouth expands to whole length of a barrel and he takes nearly whole chest are of Progo between its jaws gnawing furiously and splashing it's corrosive saliva in the process.(9 piercing damage and 5 Acid damage). As Progo's part of clothing starts to dissolve and the salive burns his skin and sharp teeth seeps into his body in places where armor does not protect him he can not longer stand the pain and looses his consciousness. The tragedy and reality of the danger hits every one of you and at this moment Tharanau spurts another burst of electricity trough his witch bolt arc, shocking the monster enough to make it loose the grip of Progo. Mimic then rolls away to C5

.

Progo starts to fade to unconsciousness at the acid and teeth sinking into his body. But just as his vision starts to fade to black, he wills himself to hold on for a moment longer. (Relentless Endurance feature to drop to 1 hp instead of 0, does the mimic still release him? Or does the electric pluse of the bolt affect Progoand take him out still?)

Progo is still released since there was a moment that you were unconscious and totally limp, even if that was a brief moment. Mimic has to act quickly as it realizes that it became the prey in this scenario instead of predator. In a one on one situation it would take te time to devour Progo completely, but now as soon as Progo did not felt like danger, he was not perceived as a danger and left out.

Goraseth sees that Progo is not dead and runs towards the creature. "Here, I said, or are you afraid ?". He then grab his weapon and tries to hit but he never fought a barrel before... where are its weak points ? he thought to himself...
Overthinking it, his attack misses as the monster keeps rolling towards his compagnons.

Action: Attack 7 (I anticipated it misses)
Mouvement to B6
Keeping concentration on Shield of Faith

Note: I think I might have had an attack of opportunity as it rolls toward Thanadau. Rolling if DM accepts. Attack 21, damage 11 (Yklwa). I'm cool with it if you rule it out. 
Note 2: nevermind... I see I stated I was at 10ft from the monster... too bad

Tryncaryn gasps as the barrel rolls towards him with viciously sharp teeth clicking and that slimy, acrid tongue flapping around. “Ugh, this vintage turned sour. I can try to distract it, but hurry!” Tryn takes an evasive stance and tries to dodge the mimic’s attacks.

(I was indeed confused with the tokens, sorry!)

Tryn gasps in shock at the speed of the mimic and how fast it dispatches his comrades, if he doesn’t act quick, he knows he’ll be the next victim for that slug of a tongue sooner rather than later. With a few quick steps he moves next to Tharanau (D4) and attacks with his quarterstaff before trying a kick (attack 18 for 4 bludgeoning and attack 9 for 4 more bludgeoning damage).

I believe you are confused with the miniatures. You are on E2 Tryncaryn (on previous map i misplaced  you to F2, fixing it on that map.) Mimic Stands next to Tharanau at this moment. It seems like you think it stands next to Tryncaryn. If that confusion is the case then you can redo your round. Otherwise we continue.

Progo lays limp for a moment as the creature seems move off to another victim (forgoing the potential opportunity attack of moving away from Progo.)

After the barrel creature rolls away Progo shambles to his feet and is dis used by the state of his garmets. He gets his shortbow out and knocks an arrow, and let's it loose.

Attack: 20 Damage: 5