Amphibious. The giant can breathe air and water.
Multiattack. The giant makes two Greatsword attacks.
Greatsword. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 30 (6d6 + 9) slashing damage.
Rock. Ranged Weapon Attack: +14 to hit, range 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 17 Dexterity saving throw, taking 54 (12d8) lightning damage on a failed save, or half as much damage on a successful one.
Spellcasting. The giant casts one of the following spells, requiring no material spell components and using Charisma as the spellcasting ability (spell save DC 17):
At will: detect magic, levitate, light
1/day each: control weather (cast as 1 action), water breathing
In my campaign I released a storm giant from captivity so it could help us fight a horde of skeletons and the servant of a vampire (a wight).
The Wight ended up casting command on the storm giant and the next turn. The storm giant rolled a nat20 on wisdom and ended up crushing the wight (which was meant to be the boss fight alongside the storm giant) on like the second turn the wight appeared