One thing a necropolis is never wanting for is bodies, either those that passed, those disposing of the dead, or foolhardy adventurers plumbing its depths. The other thing commonly found is bones, of course, and this hulking mimic hides its mass as a pile of them. It is easy enough to lay in wait, striking out when the time is right. Often times, heroes try and ‘turn’ the monstrosity. They lose precious seconds and end up devoured. The ossuary mimic can also spin off part of its mass, forming a churning mass of sharpened bone and amorphous meat that shreds stubborn prey in a much-more consumable slurry.

Ossuary Mimic

Large monstrosity (shapechanger), neutral

Armor Class 12 (natural armor)

Hit Points 110 (13d10 + 39)

Speed 15ft

Str 18 Dex 12 Con 16 Int 7 Wis 15 Cha 9

Saving Throws Str +7 SkillsStealth +7

Damage Immunities acid, necrotic

Condition Immunities prone

Sensesdarkvision 60 ft., passive Perception 12

Languages -

Challenge 6 (2,300 XP)

Shapechanger.

The ossuary mimic can use its action to polymorph into a pile of bones 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 tile 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. The tile mimic can activate or deactivate this ability as a bonus action.

False Appearance.

While the ossuary mimic remains motionless, it is indistinguishable from an ordinary pile of bones.

Grappler.

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

Actions

Multiattack.

The ossuary mimic makes two attacks.

Pseudopod.

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 4) bludgeoning damage plus 7 (1d8 + 4) piercing damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

Bite.

Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 12 (2d8 + 3) piercing damage plus 4 (1d8) acid damage.

Bone Storm (Object Form Only) (Recharge 5-6).

The ossuary mimic ejects part of its mass in a swirling mass of jagged bone shards with a radius of 20ft centered on itself. All creatures within the area of effect must succeed on a DC 15 Strength save or take 18 (4d8) piercing damage and be knocked prone. On success, the creature takes half as much damage and is not knocked prone.