Multiattack

The giant makes three Greatsword attacks, or it makes four Lightning Bolt attacks.

Greatsword

_Melee Weapon Attack:_ +14 to hit, reach 10 ft., one target. _Hit:_ 30 (6d6+9) slashing damage.

Lightning Bolt

_Ranged Spell Attack:_ +9 to hit, range 150 ft., one target. _Hit:_ 22 (4d8+4) lightning damage. If the giant scores a critical hit, the target must succeed on a DC 17 CON save or be paralyzed until the end of its next turn.

Thunderous 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 17 DEX save. On a failure, a creature takes 36 (8d8) lightning damage and 21 (6d6) thunder damage and is stunned until the end of its next turn. On a success, a creature takes half the damage and isn't stunned.