Multiattack. The giant makes two attacks; one with it's stomp and one with it's quarterstaff.

Quarterstaff. Melee Weapon Attack: +6 to hit, reach 15 ft., one target. Hit: 9 (1d8 + 4) bludgeoning damage.

Stomp. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 9 (1d8 + 4) bludgeoning damage. The target must make a Dc 13 Strength saving throw, being knocked prone on a failure. If the attack was a hit, all creatures within 5 ft of the target take 2 (1d4) bludgeoning damage.

Rock. Ranged Weapon Attack: +6 to hit, range 30/120 ft., one target. Hit: 11 (1d12 + 4) bludgeoning damage. The target must make a Dc 13 Strength saving throw, being knocked prone on a failure.