The Patient Mimic Inn is a joke. 

Literally.

Everyone has heard the gist of it. It's the one about an adventurer goes in somewhere — a tavern or maybe a dungeon — only to discover that everything is a mimic. 

It starts with the first object the adventurer touches revealing itself to be a mimic.  In a panic, the adventurer reaches for something to attack the mimic, and finds that object too is mimic.  And so that joke goes with the adventurer interacting with more and more objects as they desperately try to escape the situation, each revealed to be another mimic.

It is an absolutely absurd scenario, which is why the joke is funny.  It is also why no one believes such a scenario is actually possible.

That is, of course, until you find that the joke's on you.

The very fact that people laugh at the idea of its existence is, ironically, what perpetuates the Patient Mimic's existence and allows it to be such a successful superorganism.

The Patient Mimic is, in fact, an enormous mimic colony incorporating a house hunter mimic.  The house hunter provides shelter, protection, and transportation for its colony, while the other members typically work together to entice and capture prey.

A Night at the Patient Mimic Inn

An encounter with the Patient Mimic Inn is in reality an encounter with a mimic colony.  However, unlike the encounter described in Tasha's Cauldron of Everything, where the mimic colony is treated as a single creature representing a collective of individuals, the Patient Mimic colony should employ as many individual mimic stablocks as possible, preferably introducing a new stablock anytime a character interacts with an object of any kind.  The statistics provided above are for the Gargantuan house hunter mimic who serves as the colony's host and the final mimic encounter which is revealed if/when the party escapes from the never-ending tide of mimics within. Further statistics are provided below to represent mimics of Tiny to Large size to suit the size of objects and furniture characters interact with that are revealed to be mimics.

The both the colony as a whole and the individual host house hunter mimic have their own lair actions, and both can use one lair action each round.  The order in which they take their individual lair actions is fluid, and can be interchanged.

On initiative count 20 (losing initiative ties with other creatures), the mimic colony takes a lair action, causing one of the following effects; the mimic colony can’t use the same effect two rounds in a row:

• The mimic colony chooses up to three creatures within 300 feet of it. Each target must succeed on a DC 15 Strength saving throw or have its speed reduced to 0 until initiative count 20 on the following round, as pieces of the environment grasp the target. If a target fails the save by 5 or more, it is restrained instead for that duration.
• The mimic colony uses the Help action, aiding a creature of its choice within 300 feet of it.
• The mimic colony chooses up to three creatures within 300 feet of it. Each target must succeed on a DC 15 Dexterity saving throw or take 13 (3d8) acid damage, as orifices appear on surfaces in the environment and launch caustic spittle.
• The mimic colony chooses a cube of nonmagical, inanimate material in physical contact with it. The cube can be up to 15 feet on a side. The colony reshapes that material however it likes. This transformation lasts for 1 hour.

On initiative count 20 (losing initiative ties with other creatures), the house hunter mimic takes a lair action to cause one of the following effects; the house hunter mimic can’t use the same effect two rounds in a row:

• Form Eyestalk.  One eyestalk protrudes from a surface within the house hunter mimic.  An eyestalk is a Small monstrosity with AC 17, 15 hit points, the house hunter's ability scores, traits, and senses, and a walking speed of 0 feet.  An eyestalk can be killed by normal means.  The mimic can sense what the eyestalk senses.  Killing an eyestalk deals 15 damage to the mimic.
• Form Pseudopod.  Up to two pseudopods extrude from surfaces within the house hunter mimic.  A pseudopod is a Medium monstrosity with AC 17, 25 hit points, the house hunter's ability scores and traits, and a speed of 15 feet.  A pseudopod cannot move out of the room it was formed in.  A pseudopod uses the mimic's pseudopod attack, but with a range of 10 feet, pulling a target 5 feet on a hit, and deals only half damage.  A pseudopod can be killed by normal means.  Killing a pseudopod deals 25 damage to the mimic.  When a pseudopod is killed, the mimic automatically grows two new ones to replace any destroyed ones on the next initiative count 20, which appear in the same room as the pseudopods they replace.
• Form Maw.  One wall located inside the house hunter mimic forms a maw.  A maw is a Large monstrosity with AC 17, 35 hit points, the house hunter's ability scores and traits, and a speed of 15 feet.  A maw can only move along vertical surfaces attached to the house hunter mimic.  A maw can use the mimic's bite attack, but deals half damage, or cast acid splash as a 17th-level spellcaster (spell save DC 18, 4d6 acid damage).  A maw can be killed by normal means.  Killing a maw deals 35 damage to the mimic.
• Pseudopod Attack.  Each pseudopod inside the mimic moves up to its speed, following a pseduopod's movement rules, and makes an attack against one creature within range.  If there is no eyestalk in the same room the pseudopod occupies, a pseudopod attacks with disadvantage.
• Maw Attack.  Up to three maws inside the mimic move up to their speed, following a maw's movement rules, and make a bite attack or cast acid splash against one creature within range.  If there is no eyestalk in the same room a maw occupies, a maw's bite attack has disadvantage and a target of a maw's acid splash has advantage on its saving throw.
• Collapse (Recharge 6).  The house hunter mimic completely collapses one room that contains none of its allies inside it.  Each creature in that room must succeed on a DC 19 Strength or Constitution saving thrown (target's choice), taking 52 (8d12) bludgeoning damage and is swallowed by the mimic on a failed saving throw, or half as much damage without being swallowed on a success.  Eyestalks, maws, and pseudopods are immune to damage dealt by this action, and are not swallowed.

Everything's a Mimic

Supplemental statblocks for mimics from Tiny to Large size are provided below.

• Armor Class 11 (Natural Armor)
• Hit Points 7 (2d4 + 2)
• Speed 10 ft.

• Skills Stealth +5
• Damage Immunities Acid
• Condition Immunities Prone
• Senses Darkvision 60 ft., Passive Perception 11
• Languages Common, Telepathy 120 ft., Undercommon 
• Challenge 0 (10 XP)             Proficiency Bonus +2

Shapechanger. The mimic can use its action to polymorph into an object or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies. 

Adhesive (Object Form Only). The mimic adheres to anything that touches it. A Medium or smaller creature adhered to the mimic is also grappledby it (escape DC 11). Ability checks made to escape this grapple have disadvantage.

False Appearance (Object Form Only). While the mimic remains motionless, it is indistinguishable from an ordinary object.

Grappler. The mimic has advantage on attack rolls against any creature grappled by it.

Small monstrosity (shapechanger) , neutral

• Armor Class 12 (Natural Armor)
• Hit Points 33 (6d6 + 12)
• Speed 15 ft.

• Skills Stealth +5
• Damage Immunities Acid
• Condition Immunities Prone
• Senses Darkvision 60 ft., Passive Perception 11
• Languages Common, Telepathy 120 ft., Undercommon 
• Challenge 1 (200 XP)             Proficiency Bonus +2

Shapechanger. The mimic can use its action to polymorph into an object or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies. 

Adhesive (Object Form Only). The mimic adheres to anything that touches it. A Large or smaller creature adhered to the mimic is also grappledby it (escape DC 12). Ability checks made to escape this grapple have disadvantage.

False Appearance (Object Form Only). While the mimic remains motionless, it is indistinguishable from an ordinary object.

Grappler. The mimic has advantage on attack rolls against any creature grappled by it.

Medium monstrosity (shapechanger) , neutral

• Armor Class 12 (Natural Armor)
• Hit Points 58 (9d8 + 18)
• Speed 15 ft.

• Skills Stealth +5
• Damage Immunities Acid
• Condition Immunities Prone
• Senses Darkvision 60 ft., Passive Perception 11
• Languages Common, Telepathy 120 ft., Undercommon 
• Challenge 2 (450 XP)             Proficiency Bonus +2

Shapechanger. The mimic can use its action to polymorph into an object or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies. 

Adhesive (Object Form Only). The mimic adheres to anything that touches it. A Huge or smaller creature adhered to the mimic is also grappledby it (escape DC 13). Ability checks made to escape this grapple have disadvantage.

False Appearance (Object Form Only). While the mimic remains motionless, it is indistinguishable from an ordinary object.

Grappler. The mimic has advantage on attack rolls against any creature grappled by it.

Large monstrosity (shapechanger) , neutral

• Armor Class 14 (Natural Armor)
• Hit Points 85 (10d10 + 30)
• Speed 20 ft.

• Skills Stealth +7
• Damage Immunities Acid
• Condition Immunities Prone
• Senses Darkvision 60 ft., Passive Perception 13
• Languages Common, Telepathy 120 ft., Undercommon 
• Challenge 5 (1,800 XP)             Proficiency Bonus +3

Shapechanger. The mimic can use its action to polymorph into an object or back into its true, amorphous form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies. 

Adhesive (Object Form Only). The mimic adheres to anything that touches it. A creature adhered to the mimic is also grappledby it (escape DC 16). Ability checks made to escape this grapple have disadvantage.

False Appearance (Object Form Only). While the mimic remains motionless, it is indistinguishable from an ordinary object.

Grappler. The mimic has advantage on attack rolls against any creature grappled by it.