Shadow Elemental

Large elemental, neutral evil

Armor Class 15

Hit Points 90 (12d10+4) 12d10+24

Speed 30ft Burrow: 30ft Climb: 29ft

STR

14 +2

DEX

24 +7

CON

12 +1

INT

11 0

WIS

10 0

CHA

5 -3

Skills Stealth +10

Damage Vulnerabilities radiant

Damage Resistances cold, necrotic; bludgeoning, piercing, and slashing from nonmagical attacks

Damage Immunities poison

Condition Immunities exhaustion, grappled, paralyzed, petrified, poisoned, prone, restrained, and unconscious

Senses blindsight 30 ft., true sight 60 ft., passive Perception 10

Languages telepathy 60 ft.

Challenge 6

Shadow Form. The elemental can move through a space as narrow as 1 inch wide without squeezing. When the elemental moves through another creature's space, the target must make a DC 15 Constitution saving throw. On a failiure, the target takes 13 (2d8+4) 2d8+4 necrotic damage, or half of that on a success.
Light Susceptibility.If the elemental moves into bright light it takes 10 (2d6+3) radiant damage, and if it moves into dim light it takes half that. It takes the damage if the light is moved so it hits it as well.
Spreading Darkness.If the elemental kills a creature, it rises as a shadow elemental with half of the hit points of the original. 6d10+2 / 3d10+1 / 1d10 / 1d4 / 1d2

Actions

Tendrils of Darkness.Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 13 (2d8+4) necrotic damage.

Reactions

Opportunity. If the elemental sees an opening where light is blocked from a target, it can use the opportunity to enter the targets space, make one tendril attack, and retreat to the nearest safe spot