Corrupted Wretch

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

Unseen. While the wretch is not visible to a creature, it has advantage on attacks and grapple checks.

Skitter. The wretch can Hide as a bonus action.

Multiattack. The wretch makes two claw attacks. If both attacks hit a Medium or smaller target, the target is grappled (escape DC 13) and the wretch makes a bite attack.

Claw. Melee Weapon Attack: +7 to hit, reach 10 ft., 1 target. Hit: 8 (1d10 + 3) slashing damage. 

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft.,  grappled target. Hit: 11 (2d8 + 3) piercing damage. The wretch then heals up to half the damage dealt. 

Snatch. The wretch can extend its body up to 15-feet in any direction and attempt to grapple a creature, the targeted creature must succeed a contested grapple check or be pulled to the wretch's original position. The wretch can immediately make a bite attack on a grappled creature.