Rattling from the shadows, a gaggle of rat-gnawed bones march forward eager to slay the living. One of them lags behind, looking a bit more solid than the rest. You know your mace should have broken the leading skeletons to pieces. Yet, it merely cracked bones instead of shattering them. Tentacles lash out from the slower skeleton, adhering to you and pulling you closer to the maw manifesting from its ribcage. This is the frame mimic. The spawn of the ossuary mimic, this monstrosity also feels a kinship to the undead - specifically animated skeletons. It adopts a group of such horrors and its very presence temporarily empowers them. This is why the skeletons keep it around instead of hacking it to pieces as they would any other living thing. On top of that, frame mimics develop a supernatural stubbornness that can only be called boneheaded. So powerful is this force of will, that it mends their wounds as they plough forward against deadly spells.

Frame Mimic

Medium Monstrosity (shapechanger), neutral

Armor Class 11 (natural armor)

Hit Points 38 (7d8 + 7)

Speed 15 ft

Str 14 Dex 11 Con 12 Int 5 Wis 11 Cha 8

Skills Stealth +4

Damage Immunities acid

Condition Immunities prone

Sensesdarkvision 60 ft, passive Perception 10

Languages -

Challenge 1 (200 XP)

Shapechanger.

The mimic can use its action to polymorph into a medium skeleton 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 12). Ability checks made to escape this grapple have disadvantage.

Boneheaded Resolve.

Every time the mimic succeeds on a saving throw against a spell, it regains hit points equal to the spell's level.

False Appearance (Object Form Only).

Until the mimic makes a Pseudopod attack or Bite attack it is indistinguishable from an ordinary skeleton.

Grappler.

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

Shore Up (Object Form Only).

Undead creatures within 20ft of the mimic lose any damage vulnerabilities they have as long as they stay within 20ft of the monstrosity. In addition, these creatures also gain resistance to acid damage.

Actions

Multiattack.

Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) piercing damage.

Pseudopod.

Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) bludgeoning damage. If the mimic is in object form, the target is subjected to its Adhesive trait.

Bite.

Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) piercing damage plus 3 (1d6) acid damage.