Core Spawn Facehugger

Acidic Blood: Any nonmagical weapon that hits this creature takes a -1 to its attacks and damage rolls as the acid corrodes and destroys the weapon. At -5 the weapon completely degrades and is no longer usable as it is destroyed. All projectile ammunition are disintegrated immediately upon hit.

Shared Damage: When grappling a creature, the Facehugger takes half damage from attacks and the other half is directed towards the grappled creature. If the damage is slashing or pricing, the creature also suffers 2d6 acid damage

Resist Grapple: When a grappled creature attempts to break the grapple they have disadvantage on the roll. On a failed attempt the creature takes 2d6 bludgeoning damage.

Face Cover: While grappled by the facehugger, a creature is blinded and deafened. 

Spider Climb.  The facehugger can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Core spawn Embryo. The Facehugger implants an embryo in the abdomen of a living creature it is grappling.  While implanted the creature is unconscious as long as it is grappled by the facehugger.  Creatures  immune to diseases are immune to this Embryo.  

This embryo feeds off an infected creature’s system, killing the creature in a number of hours equal to 1d4 + the creature’s Constitution score, unless the disease is removed.   Upon dying the embryo bursts through the creature's ribcage.  If the creature was a small or medium, a core spawn crawler emerges. If the creature was large, a core spawn emissary emerges. If the creature was huge, a core spawn seer emerges. If the creature was gargantuan, a core spawn worm emerges.

This embryo can be removed with a Greater Restoration or Heal spell.

Tail Grab. Melee Weapon Attack: +3 to hit, reach 5 ft., 1 target. Hit:  4 (1d4 + 2) Bludgeoning damage. Any creature hit by the Facehuggers Tail Grab must make a DC 15 Dexterity check or be Grappled.

Implant. Melee Weapon Attack:  As a Bonus Action the facehugger can extend a tube-like proboscis down a Grappled creature's throat.  The creature must succeed a DC 15 CON save or contract the Facehugger's Core Spawn Embryo  

Scrambling Leap. If a creature moves within 20 feet of the facehugger, it can move up to its speed and make an attack with it's Tail Grab.