"well I had a good look around and didn't see anything worth taking but the others are still looking. Find anything dangerous?"

There are no traps on the stairwell leading down.

You find a further 5 days of rations and spot 3 chests in the back room. If you attempt to open one tell me left middle or right. 

Finally you are still unable to find any better gear.

"They say the best loot and the best traps wait in chests... Maybe we let the girl have a look? Hey, girl! Tilly! Come see. Is' pretty thing."

Droogan cautiously examines the chests. (Perception: 14)

The center one seems to be slightly different to the other two, which appear identical.

Different? Different how? 21 Perception.

"A lady's work in never @#$% done. Hold down the fort Yordi."

Tilly jogs up the stairs and enters the room. "What's this then? Chests? F@#$in' nice, I love chests. No one puts s$#@ in chests, that's generally a rule. You check for traps? Yeah? Nothing? Well maybes they're not trapped or maybes they're really really f@#$in' trapped. Well let's do this quick and smartish."

She runs to the other room and grabs the chain mail and slips it on over her clothes. "Either of you call dibs on this? I don't want to keep it just for this."

The cocks her head at the chests, eyeing them for anything that would give them away as trapped. She settles down to the one in the center. "Oi, biggies. If this thing sets off I want you to beat the f@#$in' s@#$ out of it immediately. Right?"

She takes out her thieves tools and goes to work. 

Slight of Hand (Dex) check 12

Valentinus can't quite tell what's wrong with it when Tilly sits down to unlock it. Resting her arm for a moment on the chest she realizes it's stuck! The chest opens to reveal rows of hideous razor sharp teeth. It's a mimic! Surprise on the party and Yordis is downstairs! (One turn to get up) 

Initiative 11

Attack: 20 Damage: 11 on Tilly. 

Initiative: 8

"Chests..."

"I'm really beginning to hate this town."

Initiative: 16.

"Motherf@#$er!" Tilly yells as she rolls back taking the razor teeth across her arm.

Initiative 15

Not great Initiative. But on her turn:

As she rolls her hands flare and throw a fire bolt at the Mimic Attack: 5 Damage: 3

Sneak Attack Damage 2 (For Droogan and Bowlder presumably being right next to the thing too.)

You have got to be kidding me with that damage on a Crit roll. Tilly is probably gonna die before her turn comes up to use this fireball anyway.

Yordis hears a commotion and turns immediately to get upstairs to help, cursing under his breath as he goes.

"What is it now!"

Initiative 18

Initiative: 20

Looks like, after the Mimic surprise round: Bowlder, Yordis, Valentinus, Mimic, Droogan, Tilly

Bowlder grabs one of the other chests, and tries to mash it into the Mimic's maw.

Improvised weapon Attack: 16 Damage: 6

Yordis runs up the stairs, charging it the room and seeing the carnage erupt. To try and avoid everyone squashing in and getting in each others way Yordis halts in the doorway channeling the radiant power of his god into a bolt of power to burn the shapechanging monster

casting sacred flame for 3 Damage (Dex 13) 

Quote from Quasimodal >>

 

Bowlder grabs one of the other chests, and tries to mash it into the Mimic's maw.

 

Valentinus pulls back out of the mimic's pseudopod range, plucks a note on his viol, and casts bane on the mimic. (Cha save DC 13).

Bonus action: He shouts to Tilly: "Keep firing like that, it won't last for long!"

Tilly gains a d6 of Bardic Inspiration.

Bowlder is the quickest to react, grabbing the chest on the right and plunging it half way down the mimic's throat. It won't be chomping on anyone for a while.

Yordis bolts up the stairs and brings down holy vengeance on the creature just before Valentinus can curse it.

Dex 21

Cha 4

The mimic the lunges at Bowlder furious as to what he did.

Attack: 14 - 4 Damage: 15

FYI: Tilly you are stuck and considered grappled. (DC 13 with disadvantage) and pulled along for a ride.

The fireball ignites the chest the monster's mouth, may wanna get out of there...

Total damage of 11 so far...

let me know if I missed something.

Droogan still has to go, but I wanted to have Bowlder's next action lined up to keep the round going.

Bowlder avoids the mimic's tentacle, but that forces him to let go of the (flaming) chest. He draws a handaxe and chops at the mimic. (Will draw his 2nd one next round for 2-fisted fighting.) Axe Attack: 20 Damage: 9

Droogan raises the Life Stealer and strikes at the mimic with a a heavy chop like splitting a log.

Attack: hitting AC 18 for 14 slashing.

"Release your treasure, filthy chest."

just to say that sacred flame is radiant not fire damage but if you think that would ignite the chest then that's up to you as DM - if it is burning then I assume it damaged the mimic on it's turn?

I  say that cause of the fire bolt that was cast, not the radiant attack.

Both the attacks land, total now at 28