Bloodphage Necromorph

Limbs. The necromorph's appendages are vulnerable to slashing damage, whether magical or not, and resistant to all piercing and bludgeoning damage. Each limb has a natural AC of 18 and has a Damage Threshold of 10 hit points that are separate from the necromorph's total hit point pool. Once a necromorph has lost at least two limbs, it's speed is halved, it cannot grapple, it's attacks have disadvantage, and the necromorph becomes vulnerable to all slashing, piercing and bludgeoning damage. It's limbs cannot be regenerated unless outside of combat and the necromorph is resting. 

Pack Tactics.  The necromorph has advantage on an attack roll against a creature if at least one of the necromorph 's allies is within 5 feet of the creature and the ally isn't incapacitated.

Ambusher. The necromorph has advantage on attack rolls against any creature it has surprised.

Undead Fortitude. If damage reduces the necromorph to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the necromorph drops to 1 hit point instead. This cannot be done if the necromorph is missing two or more limbs.

Bloodphage Infection. Whenever the necromorph's blood is spilled (by receiving piercing or slashing damage), the pray of the infected blood gives birth to 1d4 Clot Flies that spawn 5 feet from the host. This effect triggers only once per round.

Surprise Attack. If the necromorph surprises a creature and hits it with an attack the first round of combat, the target takes an additional 7 (2d6) damage from the attack.

Grappler. The necromorph may spend its two bone-blade attacks to grapple an enemy. Once grappled, the necromorph may deal an extra 12 (3d6) damage to their bite attack.
(A creature grappled by the monster can use its action to try to escape. To do so, it must succeed on a Strength (Athletics) or Dexterity (Acrobatics) check against the escape DC in the monster’s stat block. If no escape DC is given, assume the DC is 10 + the monster’s Strength (Athletics) modifier.)

Multiattack. The Necromorph Slasher can make up to three attacks. One with it's bite and two with its bone-blades.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., 1 target. Hit: 5 (1d4 + 3) piercing damage plus 2 (1d4) [Necrotic] damage. If the target is a humanoid, it must succeed a DC 14 Constitution saving throw or be infected with a disease -- Bloodphage.

While infected, the host starts to feel unwell and its speed is halved. When the host's blood is spilled (by receiving piercing or slashing damage), the spray of infected blood gives birth to 1d4 Clot Flies that spawn 5 feet from the host. This effect triggers only once per round.

Bone-Blades. Melee Weapon  Attack: +5 to hit, range 5 ft., 1 target. Hit: 6 (1d6 + 3) [slashing] damage.