Multiattack

The devil makes two claw attacks.

Betraying Carbuncle

The crystalline devil takes the form of a gemstone worth 500 gp. It radiates magic in this form, but it can't be destroyed. It is fully aware and can see and hear its surroundings. Reverting to its usual form requires another action.

Claw

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.

Crystalline Spray (Recharge 5-6)

The crystalline devil magically sprays shards of crystal in a 15-foot cone. Each target in that area takes 17 (7d4) piercing damage, or half damage with a successful DC 15 Dexterity saving throw.