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. On a failure, the zombie explodes. All creatures within 10 feet must make a DC 16 Dexterity saving throw or take 10 (3d6) acid damage. A creature killed by this damage turns into an acid zombie with hit points equal to the necrotic damage it took.

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.

Fluid Regeneration. The zombie regains 1 hit point at the start of its turn if it has at least 1 hit point.

Slam. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage plus 3 (1d6) acid damage. In addition, nonmagical armor worn by the target is partly dissolved and takes a permanent and cumulative −1 penalty to the AC it offers. The armor is destroyed if the penalty reduces its AC to 10.

Acid Breath (Recharge 6). The zombie exhales acidic fluid in a 15-­foot line that is 5 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw, taking 22 (5d8) acid damage on a failed save, or half as much damage on a successful one. The zombie then loses 5 hit points.