Undead Fortitude. If damage reduces the Aboleth Zombie 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 zombie drops to 1 hit point instead. 

Multiattack- The Aboleth Zombie can make two slam attacks, or can replace one of these slam attacks with a claw attack

Slam. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage.  

Claw. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 3 (1d6) bludgeoning damage and 2 (1d4) acid damage. On a hit, the target must succeed on a DC 11 wisdom saving throw or be enslaved by the Aboleth that created the zombie. The target is under the Aboleth's enslave ability for one minute. This effect only happens if the aboleth is within 1 mile of the victim.