Blood Armor

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

Spell Immunity. The Blood Armor is immune to three spells chosen by its creator. Typical immunities include fireball, heat metal, and lightning bolt.

Magic Weapons. The Blood Armor's weapon attacks are magical.

Artificial Vigilance. The blood armor has advantage on initiative rolls.

Innate Spell casting. The helmed horror's innate spellcasting ability is Intelligence (spell save DC 15). It can innately cast the following spells, requiring no components: 2/day each: misty step, hold person (2 creatures)

Multiattack. The helmed horror makes 2 melee attacks with its greatsword or one with its vampiric grasp.

Greatsword. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 12 (2d6 + 4) slashing damage.

Vampiric Grasp. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 8 (1d6 + 4). On a hit, the helmed horror regains hit points equal to the damage dealt.

Shockwave (2/Day). The Blood Armor smashes the ground with its fist creating a shockwave of force. Each creature in a 15-foot cube surrounding it must make a DC 15 Dexterity saving throw. On a failed save, a creature takes 2d8 force damage and is pushed 10 feet away from you. On a successful save, the creature takes half as much damage and isn't pushed.

In addition, unsecured objects that are completely within the area of effect are automatically pushed 10 feet away. 

Bonus Actions:

Bloodsnare (Recharge 4-6). The helmed horror smashes the ground with its fist and tendrils of blood spring forth and ensnare 4 creatures of its choice within 40 ft. Each creature must make a DC 15 Dexterity saving throw or be restrained. To escape, a creature must spend its action to make a DC 12 Strength or Dexterity saving throw (Dexterity saving throws are made at disadvantage due to restrained condition). 

Vampiric-Grasp. If a creature attacks the helmed horror with a melee attack as an action and misses, the helmed horror can make a vampiric-grasp attack against that creature.