Ten strange stones stand against the tides of time. Their caledonian green surfaces smoothed by erosion and scrolled with wide, curling curves devouring one another. Just beneath the soil's surface around them, one can find scores of bones; animal and humanoid. For the Circle ever hungers and its will dominates those destined to feed it. Set atop a hillside in two rough hemispheres, this megalithic structure almost looks like hands threatening to tear from the earth. In fact, in each paring one stone is stubbier than the other four. The Circle's origins are forever lost, but over generations, it has been a place of worship for sinister cults. It repays those who feed it with unholy miracles and can even manifest its will within a humanoid host for a time. One day, its gestation will finish, and sated, the Circle will sail the stars as its ancestor did. It will also leave behind a fresh clutch of ten...

The Circle

Gargantuan Construct, chaotic evil

Armor Class 14 (natural armor)

Hit Points 101 (7d20 + 28)

Speed 0ft

Str 17 Dex 9 Con 18 Int 6 Wis 14 Cha 5

Skills History +7, Nature +7, Religion +7

Damage Resistances bludgeoning, piercing, and slashing from nonmagical attacks that aren't adamantine

Damage Immunities necrotic, poison

Condition Immunities charmed, exhaustion, frightened, paralyzed, petrified, poisoned

Senses truesight 30 ft., passive Perception 10

Languages languages of creatures it possesses

Challenge 7 (2,900 XP)

Innate Spellcasting.

The Circle's innate spellcasting ability is Intelligence (spell save DC 15, +7 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

1/day each: unholy weapon

1/season each: greater restoration

1/decade each: resurrection

Regeneration.

The Circle regains 10 hit points at the start of its turn if it has at least 1 hit point.

Life Leech.

Every time a humanoid creature is sacrificed within the Circle with the express purpose of soaking its ground in blood, the Circle regains the use of one of its 1/decade spells or 1/season spells.

Actions

Multiattack.

The Circle makes two The Keening attacks.

The Keening.

Ranged Spell Attack: +7 to hit, range 90 ft., one target. Hit: 11 (2d6+4) psychic damage.

Possession (Recharge 6).

One beast humanoid that the Circle can see within 5 ft. of it must succeed on a DC 15 Charisma saving throw or be possessed by the Circle. The Circle now controls the body but doesn't deprive the target of awareness. It retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. It otherwise uses the possessed target's statistics, but doesn't gain access to the target's class features or proficiencies. The Circle can also use The Keening through the possessed body and is considered to have Detect Thoughts cast on the creature it is possessing.

The possession lasts until the body drops to 0 hit points, the Circle ends it as a bonus action, the body is moved over 1 mile away from the Circle, or the Circle is forced out by an effect like the dispel evil and good spell. The target is immune to this Circle's Possession for 24 hours after succeeding on the saving throw or after the possession ends. The Circle can only possess up to 4 creatures at a time.