Legendary Resistance (3/Day). If the giant fails a saving throw, it can choose to succeed instead.

Stone Rune. The giant has a stone rune inscribed on a mineral object in its possession. While holding or wearing the object bearing the rune, the giant can use its Prismatic Rays action.

The object bearing the rune has AC 18; 30 hit points; and immunity to necrotic, poison, and psychic damage. The object regains all its hit points at the end of every turn, but it turns to dust if reduced to 0 hit points or when the giant dies. If the rune is destroyed, the giant can inscribe a stone rune on an object in its possession when it finishes a short or long rest.

Multiattack. The giant makes three Prism Staff attacks.

Prism Staff. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit:16 (3d6 + 6) bludgeoning damage plus 13 (3d8) radiant damage.

Exploding Geode. The giant throws a geode at a point within 60 feet of itself, and the geode explodes in a dazzling flash. Each creature in a 20-foot-radius sphere centered on that point must make a DC 17 Dexterity saving throw. On a failed save, a creature takes 13 (3d8) piercing damage plus 13 (3d8) radiant damage and has the blinded condition until the end of its next turn. On a successful save, a creature takes half as much damage only. After the giant throws the geode, roll a d6; on a roll of 4 or lower, the giant has no more geodes to throw.

Prismatic Rays (Requires Stone Rune). The giant's stone rune emits beams of light that form a 60-foot cone. Each creature in that area must make a DC 17 Dexterity saving throw. For each creature in that area, roll a d6 to determine what ray affects it:

1-2: Blazing Red. On a failed save, the creature takes 35 (10d6) radiant damage and has the blinded condition until the end of the giant's next turn. On a successful save, the creature takes half as much damage only.

3-4: Dreadful Blue. On a failed save, the creature takes 35 (10d6) necrotic damage and has the frightened condition until the end of the giant's next turn. On a successful save, the creature takes half as much damage only.

5-6: Sapping Green. On a failed save, the creature takes 35 (10d6) force damage and has the incapacitated condition until the end of the giant's next turn. On a successful save, the creature takes half as much damage only.