Progo winces a bit at the tone of the kings voice. "Progo just wants to make sure Progo has all the facts. We recently saw a magical disturbance where casting a spell had a side effect of one of my companions here to sprout wings. So Progo wonders if a magical action triggered a new rug to come to life. Or someone purposely was controlling it. What did the rug look like? You say you didn't recognize it."

Just in case, Tryn starts a ritual in front of the doors to the throne room to cast Detect Magic without a spell slot, warning everyone to keep a safe distance in case something gets triggered, “I hope I the place doesn’t blow up if I cast a small spell here, might be it helps us to find the intruder.” To the king he adds, “Your majesty, let me know if  you’d rather not have me cast any spells.”

The answer is preceded with various muffled screams and mumbling:
"You all are very irritating with your questions. I will answer one last time and your audience is over. (Long pause... then a heavy sigh) I did not recognize the rug because it was not here before. It had teeth it just did not manage to bite me before i escaped. I don't care for your spells, the wild magic effects were never harmful for as long as we live here and are casting spells. Thank you and goodbye. You will be rewarded for your help."

/After ten minutes When the spell is cast everyone who is within the spell range sprouts pig's tail and their noses turns into pig snouts that squeak after every sentence the make.
Piggy elements on people gives off Transmutation magic aura that only caster can see/

“Harmless.” *squeak* “Hopefully we won’t make any precedence.” *squeak* “Let’s get moving.” *squeak* “I hope they don’t attack us on sight and turn us into ham.” *squeak* “These caverns begin to annoy me.” *squeak* he concludes before moving towards the northern corridor searching for magic auras on the way.

Northern Corridor leads to a doors with a lock but it is not locked at the moment, you go in and see a double bed and couple of other furniture. Table for to with two chairs, chest of drawers that has some decorative gnomish inventions, big rug in the middle of the room. Everything seems to be in great condition and is top shelf quality. You get the sense that it might be the royal bedroom.

Goraseth pokes every piece of furniture - the rugs in particular - with his javelin. "Nothing magical here, Tryn ?"
During the search, he also notices that his wounds are not entirely healed. He place his palm on his abdomen and whispers a old parayer to Bahamut that he heard in his childhood. Again his hand gently warms up and the bleeding cease, leaving only a tiny scar. (Using Lay on hands 3 points)

No furniture reacts to pokes.

/Nothing appears magical to Tryncaryn with detect magic spell/

“Nothing.” *squeak* “As far as I can tell.” *squeak* “Let’s keep up the pace.” *squeak* “And search the southern corridor.” *squeak*

The Dragonborn follow the halfling, poking into every single thing on the way.

Tharanau stares at the wings on Tryn's back and keeps following the others around.. And now pig snouts and tails?!? He is more scared of the effects around here than this "shapechanger".

He has also heard the same adventuring stories of biting treasure chests as Progo, so he keeps his eyes open and holds his crossbow in a ready position - he really doesn't want to cast spells. 

[rolled nature on char sheet: Nat 20.... to know about shape changy things]

Tharanau heard some stories in pubs from the adventurers that have encountered such a monstrosity. Monster that might look like a door or wall or any furniture or a simple crate. They said that whole body of it is adhesive and one of them was immediately adhered to the monster when he touched it. Monster started biting the poor fellow and he could not set himself free. They lost that man in this fight, and survived by attacking the monster from the distance and not letting him touch them. They also mentioned that their friend was devoured whole, and nothing left of him even after killing the monster, which when killed dissolved in amorphous blob.

Tharanau tells the others about the possibility that this could be a mimic -  a monster that could not be reasoned with. And he explains all the details that he has heard on his travels, warning the others about the stickiness of this thing and that it literally could be anything, even a door. 

he then proceeds to pick up gravel and dust from the path they're walking in and keeps throwing it at all the objects and walls in front of him and above him that he can see.

"Progo wonders how do you find a munching monster that's sticky and can look like anything? Progo thinks we are going to need some rocks, possibly a lot of rocks. The king said he found it between the kitchen and throne room. We should see if we can recruit a gnome to help identify potential candidates of inappropriate decor, and to show us to the kitchen!"

Also as you were walking just from Throne Room doors you Tryncaryn would detect 2 sources of divination magic and one of transmutation behind the doors on southern corridor. Upon inspecting you realize that the doors are locked.

Tryn comments the sources of magic when he notices them and goes on, “Might be that this is the vault. Anyway, I think we should break down doors, but maybe we can inquire about it.” He looks around the corner if the two inventors are still there and asks them what would be behind the southern door and if they can open the door for the party to investigate what is behind.

They do not allow you the entrance to the room. They doubt the monster is there since there is no furniture in this chamber. Other than that only they have the key so it could not get in.

They also say that you might acquire the items as a reward for destroying the monster.

If by any chance you won't find monster anywhere else they might go with you to check the chamber together, but that is an finality.

"Very well, it seems we are on our own. Let's continue. There are a couple of place we have not fully check East of those tunnels. I hope the crazy engineer is ok..." Goraseth continues his search, past the rotating spikes. Luckily he knows now how to stop them. He salutes the two gnomes in guard "Us again, we are looking for a possible monster. Kep your ears open. If you hear us scream, please come and join the fight.". If no object have been found so far, he will continue in the closest room, the one with the barrels.

Walking past the bridge, you pass Ulla. She says that Pog already took Factore to rest, and is thanks you for going easy on her. Ulla is going to check on her now as she is free of guard duty since other two gnomes changed with them. 
One of the other two gnomes who are standing guard there seems to be the one who greeted you first from the alcove. They both nod as you pass through the chamber. 
Upon entering the room filled with barrels and throwing around rocks and pebbles, you notice that upon being hit one of the barrels popped an eye out and checked what hit it. Seeing someone spotted it, it immediately overturned itself out of the row, and starts rolling your direction.

Roll Initiative! also state your position based on narrative, consider stone throwing range as 30 maximum, so the ones throwing around should be withing that range of at least one of the barrel in the room. the green circled one is the mimic.
When we state placement and initiative next battle map will be more centered on the battle i just wanted to update what have you discovered so far.

Mimic initiative = 6

Tryn initiative: 5 and position: C6 (I rolled for both in the game log, (1d4-1)*10+1d10 counted from upper left corner)

Progo initiative: 7

Position: column 3

Row: 9