Can you help me with a giant mimic?

OK, so, context.
So, I'm working on a campaign for two players, and I'm working on the end - It's called Berlin's warhammer, and I want the warhammer to be a fake inside of a giant mimic encased in the mountainside, like a big boss fight. But I need some suggestions and a stat block for it, so can you help?

The Mimic Book of Mimics definitely has something for you.

I would agree with Whatstray, the Mimic Book of mimic is a large and well-written collection of tips, stats, and other things for things exactly like what you're talking about.

I would drop some clues as they enter (weird pools of something on the ground that seem almost like - saliva? Is that an eye in the corner of my vision?) and explore the dungeon. Rearrange the dungeon as they go around (this passageway wasn't here before) and just generally make it like they're missing out on something important. mimics are always fun to play.

What sort of CR are you looking for? Difficult to make suggestions without knowing if you’re looking for something to challenge level 5 characters or level 20.

Assuming they’re not too high level the Haunting Revenant stat block in the monster manual is a CR10 living house that could easily be reskinned to be a mimic. Flee Mortals has a CR4 Bigger Mimic, and Heliana’s Guide to Monster Hunting has a variety of Tavern Mimics that are basically mimics disguised as taverns that go from CR4 to CR9

Looking to challenge my 2 level 3 players. I will be taking wolfcriedpups advice, though, even though it's just a small indent in the mountain, made for securing a warhammer. Maybe I should change it into a (living) dungeon, tho, you got anything for that?

I'll be glad to share the Google doc if you wanna help me build the boss battle ( it'll only be the boss fight since i've already printed everything out, so NO GRIEFING FOR YOU >:) )
However you'll still probably be a commentator ( you can still comment ideas and I'll place em down )

For two level 3 players you’re looking at an XP budget of either 450 for a medium encounter or 800 for a hard encounter. The standard mimic is 400xp so you could use that and just bump up its health and give it two attacks instead of just one 

I'm talking like a giant large scale mimic ( kill heart, brain, and all the other stuff ) dungeon scale mimic.

I know but you’ve still got to use a stat block of an appropriate level otherwise you’ll kill your players the first time you hit them. For instance the Bigger Mimic stat block from Flee Mortals that I mentioned can do up to 23 points of damage on a good roll which is enough to kill most level 3 characters in one hit. Flavour is free so use the stat block for a smaller mimic that’s the appropriate CR and just say it’s the size of a dungeon.

Yeah, that's pretty good! But do you think they an handle a minotaur, or a cyclops, or even a Doppleganger? Those things are in a random monster table from earlier in the campaign( they haven't visited yet.)
Anyway, do you have any monster recommendations for inside the mimic dungeon?

" I would agree with Whatstray, the Mimic Book of mimic is a large and well-written collection of tips, stats, and other things for things exactly like what you're talking about.

I would drop some clues as they enter (weird pools of something on the ground that seem almost like - saliva? Is that an eye in the corner of my vision?) and explore the dungeon. Rearrange the dungeon as they go around (this passageway wasn't here before) and just generally make it like they're missing out on something important. mimics are always fun to play. "

- Wolfecriedpup, this thread

I don't have access to anything other than the monster manual right now sorry... So please keep it within stuff I can access

If you use the Minotaur Skeleton stat block from the Monster Manual and just miss off that it’s a skeleton you might even be able to get away with two of them. Doppleganger is about right by itself but a cyclops is a bit too high level for them I think. Bear in mind that if you’re doing these encounters one after another without a long rest between them you might need to make each individual encounter easier because they’ll be using up their resources faster 

Hmm, ok! I might just use a previously made random monster generator for the dungeon (one that I made) ( and a lot more mimics than usual since it's a mimic dungeon... Do you have any ideas as for what to put in the dungeon? Here are a few of mine : 

1:A fake door that just opens up into a stomach and has a buncha teeth ( average mimic stat block )
2:Open pits in the dungeon with buncha teeth, gotta avoid them ( you can scale the wall if you fall in because of all the teeth, but you gotta make a strength check, and maybe a stealth to hide the fact that you're in it so the mimic dungeon doesn't notice )
3:A row of teeth concealing the heart, the brain, etc. that the players have to break through

The mimic book of mimics isn't an official sourcebook. It's a thread on DnD beyond by someone else that has a whole bunch of content-it's entirely free! (honestly, I think they should charge for it, it's so much and it's amazing) Link

Ye, I know, i've already looked

 Hm, I apologize, I misinterpreted. Entirely my fault.