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

Multiattack. The giant makes two greatclub attacks.

Greatclub. Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: 20 (3d8 + 7) bludgeoning damage.

Rock. Ranged Weapon Attack: +10 to hit, range 60/240 ft., one target. Hit: 29 (4d10 + 7) bludgeoning damage. If the target is a creature, it must succeed on a DC 17 Strength saving throw or be knocked prone.