Brain Seeker Zombie

Zombie Fortitude.  If a hit brings a zombie to less than 0 HP, the Zombie can roll a CON save of DC 10 + Damage past 0.  If the zombie succeeds, it remains alive with 1 HP. 

Absence of Intellect. Any spell or magical effect requiring an INT/WIS check has no effect on the zombie. 

Crit Crusher.  If the Zombie scores a critical hit on a target, the target is also grappled and the Zombie has advantage on its next attack unless the grapple is broken.

Multiattack. The zombie makes two attacks: one with its claws and one with its bite.

Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 8 (3d4 + 1) slashing damage.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 13 (3d8) piercing damage.

Crit Crowd.  As a reaction to an enemy being hit by a Critical Hit within 20' of it, the zombie may react by moving 10' and making 1 claw attack if possible to the enemy that was hit by the critical.