I've been DM (off and on) for a long time, and in all those years, I've NEVER used a mimic. It seemed like something lame that would get annihilated after a couple rounds with no backup, as they are written as solitary hunters. But I was running a level of the Dungeon of the Mad Mage and they included one. I read it and thought, "that just might work", so I left it in. 

In this case (spoilers) the mimic is a small rowboat, on a river. Out in the open, no threats in sight. About to start a long rest, the party splits up and does/checks a few things, and a couple players decide to check out the pier and rowboat. One steps in and the mimic reveals itself with a big chomp, and drifts away from the dock. Moving into the stream the mimic rolls over and now the PC is underwater and in danger of drowning. The second PC jumps onto the floating creature and melee ensues. It was a grand fight with swords, teeth, water, blood and pseudopods everywhere, that came this close [   ] to killing a PC. After playing the scenario I realized that with mimics, it's all about location, location, location. 

So maybe a span of a small bridge over a crevasse or other scenarios where the location itself is as much of a danger as the big chomp itself.

What are the best ways you guys used a mimic? Do tell.

My favorite mimic is one that, when it dies, spits up two magical-looking items...which are two more mimics, which do the same thing, and so on. I call it the Greed Mimic. Players have died to it, convinced that it won’t go on forever.

I use it as a cup sometimes, because of it's adhesive effect anything that touches the cup to find out what's in it will be grappled BY A CUP, it's hilarious to watch the players faces as you reveal that the random mug of ale was a mimic

the only time I've used one was as a breastplate, I ran it as being able to control its adhesive side, so once the breastplate was strapped onto the unlucky PC the adhesive stuck the breast plate to them and then had teeth and eye balls and tentacles pop out and start the carnage as they have to fight the mimic and not hit the person wearing it.

That specific mimic is a ton of fun!

I ran a bunch of homebrew mimics masquerading as a small village. My idea was that they slowly moved into a town posing as smaller things, pieces of farm equipment, doors on buildings, an outhouse or shed, stuff like that, and they slowly eat the villagers and set up shop to pick off travelers who come through the town. When the PCs arrived, everyone was dead. 

On the way into town the PCs were attacked by a bunch of tiny mimics disguised as pebbles on the road. Once they got into town there were buildings with extra doors and other goofy things like that to let them know that something was off. The Ranger immediately fired at one of the doors - *thud*, nothing - and then fired at the one adjacent - *the door lets out a guttural scream*.  That was good for a laugh, and after the 10-minute double door hunt they decided to poke around. Inside houses were mimic beds, mimic bookshelves, mimic books, even a group of tiny mimics disguised as a pile of coins that could fling themselves up to 10 feet, and piles of bones scattered around in various places.  The big ending was a gargantuan mimic disguised as an entire house that was able to collapse its rooms and swallow anyone inside.

It was a really goofy session but my players loved it since it was a thematic break from a meat grinder that they had been in for awhile. From the moment they checked their map and realized there wasn't supposed to be a town here to the suspense of not knowing which objects would be mimics and which were real, there was a great mix of camp and suspense that played really well. 

Okay. My player's barbarian befriended a mimic named Grogger, in the first session, so the rule that Grogger takes his turn on the Barbarian's turn.

And how my friend used him is basically using Grogger as he takes the form of one of his throwing weapons, he'll yeet them on the enemy and Grogger will pin them down with his weight.

https://www.dndbeyond.com/forums/dungeons-dragons-discussion/dungeon-masters-only/18708-the-mimic-book-of-mimics

During character creation, one of my players told me that his character  had " A lock that opens only when blood is dripped in the keyhole" . Apparently he found it on the list of Gothic Trinkets from the Curse of Strahd.  Since this wasn't something I had planned to include in my homebrew world.... baby mimic.

I did a Pool Table mimic in the middle of a haunted abandoned mansion and did everything i could to make it seem like it was supposed to be a puzzle or something. and when the bard was trying to be all flirty with another character by doing the classic "Lemme show you how to play" and leaned on the table, a mouth opened up and attacked lol

Quote from RoscoFatrabbit >>

https://www.dndbeyond.com/forums/dungeons-dragons-discussion/dungeon-masters-only/18708-the-mimic-book-of-mimics

 Rosco, thanks very much for posting that. I'd no idea it existed. Great stuff.

Just an idea: My favorite mimic (as a player, NOT as a character), was one that a DM threw at my party many years ago. This was back in the late 80s, maybe early 90s. The party was slogging down this muddy road, on foot, during the rainy season, just trying to get to the next town. All of a sudden we came upon a stretch of road that wasn't mud! It was a stretch of flat, solid, stone road! Fifteen feet wide, maybe 100 or so feet long. So of course we enjoyed walking along a nice solid surface for a moment.... until... the edges of the stone road surface began curling up and in, and we realized we were about to fight our way out of a massive f*cking mimic. 

All it takes is one mimic, and for the rest of the campaign, every member of the party will be suspicious of literally every single inanimate object they encounter! 

OH! Sorry, I just had an idea! Don't tell anyone! What if...??? What if there was some new kind of homebrew kinda mimic, which is actually like a collective of many tiny mimics. And what if they live inside a chest or a bag in a dungeon. So the party gets suspicious of the chest they found... they inspect it... they poke it... nope, it's definitely not a mimic. Okay, so they open the ordinary chest to find it full of gold coins! So one character reaches their hand into the coins.... BOOM! Each coin is a tiny mimic! Each has a tiny mouth that nips you for 1 hp of damage each. But with so many it's like sticking your hand into a fish-tank full of piranha!

Don't tell anyone!

One idea I had was that a mimic could be dormant as a piece of armor or a weapon and when it gets swung or gets hit it wakes up and adds to the chaos!

Another was to have it disguised as an apple or a small piece of food and well... if a character trys to eat it... 

I used that same mimic in Dungeon of the Mad Mage. I told the group that a rowboat was drifting closer to them about 3 times. They did nothing but watch it. It managed to almost drown one of the party members. 

Some mimics I have used are the following:

• One that covered up a pit trap, matching the stone floor next to it. The magic of this that the floor is probably the last place the party would expect a mimic. Once a party member or two step onto the mimic, it grabs them, moves itself to the other side of the pit trap, and keeps the other members from jumping across by blocking the hallway, forcing any jumpers into sticking into it, or falling down the pit trap (spikes at the bottom are recommended).
• A well, in the middle of a ghost town. The mimic was planted as a curse by a local hag, or some other sinister creature. If the party looks down the hole beneath the well, they see the bones of all the dead town residents.
• A trapdoor or barrel inside a storage room of the dungeon. 

Backpack mimic

Everything the characters chuck in their backpack gets eaten including their rations then a couple of days later they are starving to death.

I like giving my mimics some sort of fire-breath so they can pose as chandeliers or candles. Imagine trying to fight a fire-spewing chandelier that keeps bouncing down and back up from the ceiling using a bungee-cord tendril.