This particular strain of mimics was carefully cultivated into being by a drow matron sick of uninvited guests - both of the adventurer and political rival variety. Resistant to pesky bypassing magic and capable of alerting a building's occupants (and other mimics) of interlopers, entry mimics became all the rage... well, until they started eating honored guests and the occasional house pet. The matron quickly lost favor and stepped through one door never to return... as it were.

Entry Mimic

Medium monstrosity (shapechanger), neutral

Armor Class 14 (natural armor)

Hit Points 58 (9d8 + 18)

Speed 15 ft

Str 20 Dex 13 Con 15 Int 5 Wis 14 Cha 8

Saving Throws Str+7

Skills Stealth +5

Damage Immunities acid

Condition Immunities prone

Sensesdarkvision 60 ft, passive Perception 12

Languages understands All but cannot speak

Challenge 3 (700 XP)

Shapechanger.

The mimic can use its action to polymorph into a door 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 grappled by it (escape DC 15). Ability checks made to escape this grapple have disadvantage.

Ding Dong (Object Form Only).

When the mimic is opened, it may telepathically alert a creature that resides on the other side that is within 500ft that it has been opened.

False Appearance (Object Form Only).

While the mimic remains motionless, it is indistinguishable from an ordinary door.

Grappler.

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

Gatekeeping (Object Form Only).

If the mimic is targeted by a magical ability that would bypass it such as Knock, Passwall, or the like it makes a Strength save against the effect using the spell caster's appropriate spell DC. On success, the user of the ability is teleported 30ft closer to the mimic. If this ability moves the caster within 5ft of the mimic, the mimic may use its Bonus Action to make a Bite attack against the creature. On failure, the mimic is forced to Shapechange back into its true form.

Actions

Pseudopod.

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) bludgeoning damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

Bite.

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) piercing damage plus 4 (1d8) acid damage.

Reactions

Bell Ringer.

When the mimic critically hits a target with one of its attacks, it may use its reaction to make a Pseudopod attack against that target.