How Large Can A Mimic Get? My Thoughts

In many forms of entertainment, such as tabletop games, video games, amongst others, we recognize a wide menagerie of creatures, monsters, and enemies that a hero or group of  heroes has to overcome.  Such enemies include the classic street thugs of the classic video game, the wizards and orcs of tabletop games, such as Dungeons and Dragons, and many others.
But there is one type of monster that is, with a good mix of creativity, can be both really fun and equally horrifying to play against.  That monster is the mimic.
We both love and hate this creature, because it is both awesome, with it’s great teeth filled maw, and love of deceiving us with it’s seemingly harmless shape when we first encounter it.  The mimics that I’m referring to will be the ones we typically come across in Dungeons and Dragons.  Most mimics in other forms of media and entertainment can be included as well I suppose, but I want to talk specifically about the ones found in the classic tabletop game.
The reason for this is, most other forms of media where they are found are usually one type of object – a treasure chest.  Those are great and classically sinister versions of the creature, but that’s the problem, that’s the only form we typically ever see, a lot of times, even in D&D.  I’ve come across a variation or two of the mimic during my time playing the game, such as barrel mimic.  That was always fun, but really, it’s still fairly close to the classic chest that a mimic, well, mimics.
About six months to  year ago, I started thinking of all the different and fun types of mimics you could possible come across, such as the barrel mimic, but I soon wanted more.  I began scouring the interwebs for some awesome image of the hungry, tooth-filled creature, and found quite a few.  But of course, the most common type was – you guessed it – the treasure chest.  I wanted more.
I had been playing a lot of Dark Souls, and encountering my fair share of mimics, and with that in mind, I began looking for Dark Souls mimic through Google image search.  Low and behold, I ended up finding some pretty kick as images of mimics I never would have thought of.  I found some sample art of ladder mimics, bonfire mimics, amongst others.  It was a scary thought that there could be a larger variety of the mimic out there.
That got me thinking – if a mimic could take the shape of so many different types of objects, what else could it be, and more importantly, how large could they get?  The initial thought was pretty spooky, as a large, or monstrously sized mimic could be a horrific thing to take on.  If there was such a large mimic out there to encounter in the world of D&D, how creative could you be when creating one?  How large could they get?
As I began thinking about it, a wonderful idea sprang to mind late last year, before Halloween, I wanted to run a game for the scariest time of year.  But what should I do?  Should I do the classic haunted house?  A gothic setting with werewolves or vampires?  Naw.  I settled on a fun idea – a game were I would lead my players though a house full of several types of mimics, such as rugs, ovens, and even a giant pipe organ, and they’d have to find their way out with their lives intact.  But there was a catch.  It wasn’t just a house of mimics, oh no.  How would anybody get a bunch of mimics together in the same place, let alone in the same building?  You’d have to have a death wish to get that many of them in one spot.
I figured that the house wasn’t just an ordinary house.  The house itself was a giant mimic.  To be specific, it was a it was a Mimic Hive.  It was both mother and caretaker to all the smaller and younger mimics found within itself.  It was an older creature, something that had found a way to live throughout the years, and grow beyond the size of a typical item like a barrel or a chest.  It had earned the right to be as large as it was, and have mimic children of its own (mimic children – that thought made me laugh as I wrote it).
But I don’t think it should stop there.  Why would the size of a mimic need to end at the size of a house or typical building?  I want to think bigger, grander than that.  What about a fortress or castle mimic?  Could you imagine, an entire castle, which could be inhabited with people, as mimic?  What would it look like if it came alive?  How powerful would a monster of that size be?  But let’s get even larger than that.  Much, much larger.
What about something the size of a landmass, or even the planet itself?  How would something like this even exist?  I’m not sure how it would work, but I can imagine that a planet sized mimic would be similar to the head of Unicron from Transformers.  It would be the mimic devourer of worlds, and we would just be parasites living on the skin of that mimic.
I’m sure that the logistics of a mimic the size of a landmass, such as a continent, or even a mimic who IS the planet, would be scoffed at by many, saying it may not be logical even from a fantasy standpoint, but I think it could be something for people to look into if they wan’t to inject something fun or different into their game.
What are your thoughts on this?  How large would you take your mimics?  Would they be larger than even a planet?  How would it work in this case?  Let me know!