Wall Thing

Amorphous. This shadow-like creature can move through a space as narrow as 1 inch wide without squeezing.

Shadow Stealth. While in dim light or darkness, the shadow can take the Hide action as a bonus action.

Sunlight Weakness. While in sunlight, the shadow has disadvantage on attack rolls, ability checks, and saving throws.

More. If a non-evil humanoid dies from this creature's attacks, a new shadow rises from the corpse 1d4 hours later.

Spike. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 6 (2d6-2) piercing damage. The first time a creature is attacked with this, it is done with advantage if done from its shadow form.

Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 6 (2d6-2) slashing damage.

Shadow Movement. This creature can move up, down, and across vertical surfaces and upside down along ceilings, without using any appendages. The movement is often rapid and surprising, granting advantage on attacks against creatures when used in conjuction with its Reform or its Spike form.

Reform. As a bonus action, this creature can extrude itself outward into a haunting version of itself from when it was mortal. This form can be in full, just its head, or its entire upper body even hanging from the wall or ceiling. Any beast or humanoid that sees this behavior must succeed on a DC 12 Wisdom saving throw or become frightened of the creature for 1 minute. The frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. A creature that succeeds on a saving throw against this ability is immune to this ability for 24 hours.