Enveloper

An AD&D monster adapted to 5e

A failed experiment. A flesh golem filled with life not bestowed by its master. Then it consumes its master. A mass of malleable flesh, it continues to consume creatures, pulling them into its fleshly form. Like being at the center of a naked, sweaty dogpile, its victims are superheated and melted by the pressure and heat. Its victims become one with its form. 

The Enveloper learns and grows and it consumes. It can learn languages, spells, and martial techniques from those it assimilates. In theory, if one is let live for too long, it will continue to grow until it is unstoppable.  

Monster stat block

ENVELOPER 

Large aberration, Unaligned

Armor Class 12 (natural armor)

Hit points 145

Speed 15 ft.

Damage Resistances bludgeoning

Condition Immunities charmed, frightened, paralyzed, petrified, prone, restrained, stunned 

Senses blindsight 60 ft.

Languages all known by the creatures consumed

CR Roughly 5

Consume. Envelopers can digest dead creatures and organic matter in whole, if it spends one round doing so. Clothes, weapons, and other equipment are inedible to an enveloper.

Absorb. Three rounds after consuming a creature, the enveloper permanently absorbs the abilities, knowledge, and skills of the creature. This absorption includes the sum of that creature's experience, personality, intellect, and the ability to speak with that creature's voice. 

The Enveloper increases it’s hit point maximum and current HP value by one hit die of the absorbed creature. Additionally, the enveloper gains one trait from the absorbed creature, such as a language or tool proficiency, spell, or class ability.  

Amorphous. An enveloper is not subject to critical hits. It has no clear front or back, so it cannot be flanked.

Grasping Tentacles. The Enveloper can have up to five tentacles at a time. Each tentacle can be attacked (AC 12; 10 hit points; immunity to poison and psychic damage). Destroying a tentacle deals no damage to the Enveloper, which can extrude a replacement tentacle on its next turn. A tentacle can also be broken if a creature takes an action and succeeds on a DC 15 Strength check against it.

ACTIONS

Multiattack. The Enveloper can make three Tentacle Slam attacks and choose to Envelope one grappled creature

Tentacle Slam. Melee Weapon Attack: +7 to hit, reach 30 ft., one target. Hit: 2d6 + 4 bludgeoning damage, and the target must pass a DC 13 Dexterity saving throw or be grappled. Until this grapple ends, the creature is restrained.

Envelope. The enveloper can choose to retract its tentacles into its form, pulling a constricted creature into its form to be melted down under the heat and pressure of its molten flesh form. An enveloped creature is restrained and can not see, hear, or breathe. On the enveloped creature’s turn, it takes 2d10 fire damage and can make a DC 15 strength saving throw to try and escape. The Enveloper can have up to two creatures Enveloped at a time. 

Absorbed Abilities

Originally I designed the monster to be even more cruel. Feel free to add these on to the Enveloper if it needs a boost. 

Resinous Solvent. This creature excretes a glue-like substance. Any weapon attack or unarmed strike made against it will stick to the creature automatically. You can attempt to remove a stuck object with a successful DC 13 strength check. The solvent can be burned away, or washed away in water. This causes the Enveloper to gain a damage vulnerability to fire

If you think your enveloper may have already encountered and consumed some enemies, consider looking through the tables on 280-281 in the Dungeon Master’s Guide to assign additional abilities. 

History, changes, design philosophy

The Enveloper was featured in TSR’s Field Folio (1981) as a large marshmallow man that seeks to knock its victims down so it can fall on them and consume their form. When I originally read this, I found the concept fantastic but the form silly. I wanted this to be a creature that the players see and say “nah, we’re good”. Using its main mechanics of pulling creatures into its form to be assimilated into its form, I grafted that over the Roper stat block from the Monster Manual and made adjustments. This thing is nasty in both appearance and combat. It is slow and chunky. Your players should be able to hit it easily and often. The Envelopers defense against this is its large health pool and ability to restrain most of the party in a turn. I would not design an encounter where this thing has other baddies to fight alongside, unless it plans to consume them as well.