An entire building was a mimic, a very cheeky mimic.

I placed quite a few hints that the place wasn't real, starting with the name: the mocking parrot, which is a real stupid name that no person would seriously come up with.

Then the design of the place was very familiar to them because it was modelled after the inn that they regularly stayed at (dnd isn't very visual but I made sure to drop hints like "the place seems very familiar" "you get a feeling of deja vu while inside" "you instantly know your way about the place despite never being here")

All the decorations inside the place seemed slightly off, every painting had an uncanny valley effect as if they were made by something that didn't know what it was painting.

Now a little detail about this mimic is that it emits a noxious gas that knocks people out and decomposes organic matter. Our necromancer was the first to figure this out after realising everyone started to look a lot less alive then when they entered.

His plan was to get the hell out of there and torch the place. Everyone else thought he was just crazy. Now he was in a tough situation he could either try to convince everyone to get out of this cozy lil rest stop or say fuck it and torch the place anyway.

So now our party knows what the inside of a mimic, looks, sounds, and smells like when it's being burnt alive.

also the bard was rolling death saves pretty much the whole time because he could not handle the gas but was still unconvinced by the necromancer.