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.

Corrosive. Any nonmagical weapon made of metal or wood that hits the zombie corrodes. After dealing damage, the weapon takes a permanent and cumulative −1 penalty to damage rolls. If its penalty drops to −5, the weapon is destroyed.

Death Burst.  When the zombie dies, it explodes.  Each creature within 15 ft. of it, must make a DC 13 Dexterity saving throw, taking 14 (4d6) acid damage on a failed save, or half as much damage on a successful one.  On a failed save, a creature is covered in acid, causing it to take 9 (3d4) acid damage at the start of its turns.  The affected creature or another creature within 5 feet of it can use an action to scrape the acid off, therefore ending the effect.  

Corroding Slam. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage plus 10 (4d4) acid damage.  The target must succeed on a DC 11 Constitution saving throw or it takes 5 (2d4) acid damage at the start of its next turn.  

If the target is wearing armor made out of metal or wood, the armor takes a permanent and cumulative -1 penalty to AC.  The armor is destroyed if the penalty drops the armor's base AC to 0.  

Hurl Acid.  Ranged Spell Attack:  +5 to hit, range 60 ft., one target.  Hit:  7 (2d6) acid damage, and the target takes 2 (1d4) acid damage at the start of its next turn.   

Splat (3/day).  When the zombie takes damage, it can choose up to three creatures within 10 ft. of itself.  Each creature that was targeted by this ability must make a DC 13 Dexterity saving throw, taking 6 (1d12) acid damage on a failed save, or half as much damage on a successful one.