Blood Elemental

Incomprehensible: Because of its alien mentality, a blood elemental does not understand verbal communication of any sort, nor can its own gurgling language be understood by any creature except its own kind. A blood elemental is immune to all language-dependent spells and effects, and no mundane or magical effect that usually allows verbal communication (including a tongues spell) functions with respect to it. If anyone reads the thoughts of a blood elemental, they automatically suffer the effects of a Feeblemind spell, no save permitted.

Blood Form. The elemental can enter a hostile creature's space and stop there. It can move through a space as narrow as 1 inch wide without squeezing.

Freeze. If the elemental takes cold damage, it partially freezes; its speed is reduced by 20 feet until the end of its next turn.

Bloodbath:

Each creature in the elemental's space must make a DC 15 Strength saving throw. On a failure, a target takes 13 (2d8 + 4) bludgeoning damage. If it is Large or smaller, it is also grappled. Strength (Athletics) or Dexterity (Acrobatics) DC 15 to escape. Until this grapple ends, the target is restrained and unable to breathe. If the saving throw is successful, the target is pushed out of the elemental's space.

The elemental can grapple one Large creature or up to two Medium or smaller creatures at one time. At the start of each of the elemental's turns, each target grappled by it takes 13 (2d8 + 4) bludgeoning damage. A creature within 5 feet of the elemental can pull a creature or object out of it by taking an action to make a DC 15 Athletics Check and succeeding.

A victim that is still alive when it emerges from the blood elemental's body takes 4d6 psychic damage and must make an Intelligence DC 17 saving throw. On a failed save, the creature's Intelligence and Charisma scores become 1 as the Feeblemind spell because of the strain on its sanity that the sensation of drowning in blood produced. Furthermore, the victim creature must make a successful Constitution save DC 17 on emerging or be poisoned for 2d6 rounds.

Multiattack.

The elemental makes two slam attacks.

Slam. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage.

Further, the victim of such an attack must make a Constitution Saving Throw DC 15 or have a portion of their own blood drawn forth from their body and added to that of the elemental. The amount of blood lost in this way is equal to the damage done by the initial blow. Thus, an attack that inflicts 12 points of damage is followed by a potential blood drain that inflicts an additional 12 points of damage. Hit points lost to the blood drain are added directly to the elemental’s own hit point total.