Undead Fortitude. If damage reduces the 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.  

Shroud of Spores.  The zombie is surrounded by a cloud of toxic spores, permanently granting it the effects of a spirit shroud spell.  A creature that takes this damage is poisoned until the end of its next turn.  Creature's take this damage when they start their turn within 10 ft. of the zombie or hit it with a melee attack.  A creature also takes this damage, if starts its turn grappling the zombie.     

Death Burst.  When the zombie dies, all creatures within 30 ft. of it must make a DC 14 Constitution saving throw, taking 11 (2d10) necrotic damage on a failed save, or half as much damage on a successful one.  On a failed save, a creature is infected with the disease described in the Infecting Touch attack.  A creature killed by this attack rises up as a zombie, as well as any corpses in the affected area.  Any undead in the area gain temporary hit points equal to half the damage this trait dealt.          

Infecting Touch. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage plus (4d6) poison damage.  If the target is already poisoned, it must succeed on a DC 14 Constitution saving throw or become poisoned for a number of hours equal to 1d10 - the creature's Constitution modifier.  While poisoned in this way, a creature has disadvantage on Constitution checks and Death saving throws, and it gains one level of exhaustion.  A creature killed by this attack rises up as a infectious zombie on its next turn, as well as if a creature dies while poisoned in this way.          

While poisoned in this way, a creature must make a DC 16 Constitution saving throw at the start of its turns, taking 3 (1d6) poison damage on a failed save, and ending the effect on a success.  A creature that takes this damage has its hit point maximum reduced by the amount of damage taken.  This reduction lasts until a creature finishes a long rest.  Even if this effect ends, all other effects of the poison remain.