Infectious blood

If a creature would take necrotic damage from abyssal spawn and fails a (DC 14) Constitution save, whenever that creature regains hit points, they regain half those hit points instead. The effects ends if they take a short or long rest. 

Explode

As an action, the abyssal pawn can explode. All creatures within 5ft of it must make a (DC 15) Dexterity check and take (3d10+5) necrotic damage. Half on a succesful save, then make a (DC 14) Constitution or be poisoned for one hour. The abyssal spawn dies after this action. 

Multiattack. The Abyssal pawn can make two slam attacks

Slam. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage. 

Spit. Ranged Weapon Attack: + 4 to hit, reach 30/60 ft., one target. Hit: (3d6 + 4) necrotic damage. Con save (DC 14) or poisoned for 1 hour.