Monster Manual, page 156
Stone Camouflage. The giant has advantage on Dexterity (Stealth) checks made to hide in rocky terrain.
Multiattack. The giant makes two greatclub attacks.
Greatclub. Melee Weapon Attack: +9 to hit, reach 15 ft., one target. Hit: 19 (3d8 + 6) bludgeoning damage.
Rock. Ranged Weapon Attack: +9 to hit, range 60/240 ft., one target. Hit: 28 (4d10 + 6) bludgeoning damage. If the target is a creature, it must succeed on a DC 17 Strength saving throw or be knocked prone.
Variant: New Giant Options
Some adult stone giants like to grab enemies and fling them through the air. They can also roll boulders across the ground, striking multiple enemies in a line. These abilities are represented by the following action options.
Fling. The giant tries to throw a Small or Medium creature within 10 feet of it. The target must succeed on a DC 17 Dexterity saving throw or be hurled up to 60 feet horizontally in a direction of the giant's choice and land prone, taking 3 (1d6) bludgeoning damage for every 10 feet it was thrown.
Rolling Rock. The giant sends a rock tumbling along the ground in a 30-foot line that is 5 feet wide. Each creature in that line must make a DC 17 Dexterity saving throw, taking 22 (3d10 + 6) bludgeoning damage and falling prone on a failed save
Source: SKT, page 246
Rock Catching. If a rock or similar object is hurled at the giant, the giant can, with a successful DC 10 Dexterity saving throw, catch the missile and take no bludgeoning damage from it.
Hill, Mountain, Underdark