Blood Golem

Amorphous.  The blood golem can move through a space as narrow as 1 inch wide without squeezing.

Blood Ooze. The blood golem takes up its entire space. Other creatures can enter the space, but a creature that does so is subjected to the blood golem’s Engulf and has disadvantage on the saving throw. Creatures inside the blood golem can’t be seen and have total cover. A creature within 5 feet of the blood golem can take an action to pull a creature or object out of the cube. Doing so requires a successful DC 12 Strength check, and the creature making the attempt takes 10 (3d6) necrotic damage. The blood golem can hold only one Large creature or up to four Medium or smaller creatures inside it at a time.

Blood Sense. The blood golem can magically sense the presence of blood in living creatures up to 1 mile away. It knows the general direction they’re in but not their exact locations.

Blood Splatter. Any time the golem is hit in combat, a gout of blood erupts from its body. All creatures within 10 feet of the golem must succeed on a DC 15 Dexterity saving throw or be blinded until the end of the creature’s next turn.

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.

Multiattack. The golem makes two slam attacks or one slam attack and one engulf attack

Slam. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage, and the target must make a DC 15 Constitution saving throw. On a failed save, the target takes 14 (3d6 + 4) necrotic damage; its hit point maximum is reduced by the amount equal to the necrotic damage, and the blood golem regains hit points equal to that amount. On a successful save, the damage is halved and the golem regains no hit points. The reduction in the target’s hit point maximum lasts until the target finishes a short or long rest. The Golem's target dies if this reduces its hit point maximum to 0.

Engulf. The blood golem attempts to engulf a Medium or smaller creature within 10 feet of itself. The creature must make a DC 15 Dexterity Saving throw or become engulfed. On the turn it is engulfed, the creature suffers 10 (3d6) necrotic damage. The engulfed target is blinded, restrained, and unable to breathe, and it must succeed on a DC 15 Constitution saving throw at the start of each of the golem's turns or take 21 (6d6) necrotic. If the blood golem moves, the engulfed target moves with it. The mound can have only one creature engulfed at a time. An engulfed creature can break free by using its action to succeed on a DC 13 Athletics Check.