Blood Golem of Hextor

Necrotic Absorption. Whenever the golem is subjected to necrotic damage, it takes no damage and instead regains a number of hit points equal to the necrotic damage dealt.

Immutable Form. The golem is immune to any spell or effect that would alter its form.

Magic Resistance. The golem has advantage on saving throws against spells and other magical effects.

Magic Weapons. The golem's weapon attacks are magical.

Blood Sense. The golem can sense the location of any creature that is not a construct or undead within 1 mile of itself.

Blood Necessity. The golem must consume 1 gallon of blood every 24 hours or it will gain 1 level of exhaustion it is not immune to.

Death Throes. When the golem dies, it explodes, and each creature within 30 feet of it must make a DC 20 Dexterity saving throw, taking 70 (20d6) necrotic damage on a failed save, or half as much damage on a successful one. 

Multiattack. The golem makes two melee attacks.

Bite. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 20 (3d8 + 7) piercing damage.

Flail. Melee Weapon Attack: +13 to hit, reach 15 ft., one target. Hit: 23 (3d10 + 7) bludgeoning damage.

Blood Siphon (Recharge 6). The golem drains blood from creatures in a 15-foot cone. Each creature in that cone must make a DC 19 Constitution saving throw, gaining one level of exhaustion and taking 28 (7d8) necrotic damage on a failed save, or not gaining exhaustion and taking half as much damage on a successful one. constructs and undead are unaffected. The golem regains hit points equal to half the damage dealt to all creatures affected.