Multiattack. The giant makes two attacks with its greatsword or hurls two rocks.
Greatsword. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit:30 (6d6 + 9) slashing damage plus 18 (4d8) necrotic damage.
Rock. Ranged Weapon Attack: +14 to hit, reach 60/240 ft., one target. Hit:35 (4d12 + 9) bludgeoning damage.
Lightning Strike (Recharge 5–6). The giant hurls a magical lightning bolt at a point it can see within 500 feet of it. Each creature within 10 feet of that point must make a DC 15 Dexterity saving throw, taking 54 (12d8) lightning damage on a failed save, or half as much damage on a successful one.