The creature stands next to the dead antelope, its humanoid form made of light-blue crystalline material. The head of the creature shifts and slowly grows two black horns.

An Impossible Imposter. The xenabsorber’s body is comprised of magically-attuned blue crystal. When it vibrates on the same magical frequency as a nearby creature, it can change itself to copy some aspect of that creature. Given enough time, it can turn its entire form into that creature, though fine details elude it. The xenabsorber becomes agitated if it stays in one form too long, so it is always on the move, looking for new creatures to copy.

A Grotesque Amalgam. At any given moment, the xenabsorber might be in its native blue crystalline state, fully disguised as a creature, or wearing aspects of many different creatures. In areas with high traffic of a variety of creatures, the xenabsorber might be a physical representation of the presence of or conflict between all of those creatures.

Xenabsorber

Medium aberration, chaotic neutral
Armor Class 15 (natural armor)
Hit Points 65 (10d8 + 20)
Speed 30 ft.

STR	DEX	CON	INT	WIS	CHA
17 (+3)	12 (+1)	15 (+2)	10 (+0)	13 (+1)	15 (+2)

Skills Deception +4, Perception +5
Senses darkvision 60 ft., passive Perception 15
Languages Common
Challenge 3 (700 XP)

Disguise. The xenabsorber has advantage on Charisma (Deception) checks to pass itself off as the type of creature it is impersonating as long as it has at least 1 trait from that creature.

Trait Mimicry. As a bonus action, a xenabsorber can take on 1 nonmagical physical trait, attack, or reaction of a beast or humanoid with a challenge rating equal to or less than its own that it has seen within the last week (see Trait Mimicry sidebar). It can have up to 5 such traits at a time, no more than two of which can be attacks. Each trait lasts until the xenabsorber replaces it with another trait as a bonus action. If the xenabsorber goes a week without exposure to a single beast or humanoid, it loses all of its traits and reverts back to its true, blue crystalline form.

Actions

Multiattack. The xenabsorber makes two melee attacks.

Slam. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (1d10 + 3) bludgeoning damage.