The crystal dragon

Gargantuan dragon, neutral

Armor Class 19

Hit Points 348

Speed

STR

22 +6

DEX

9 -1

CON

20 +5

INT

12 +1

WIS

13 +1

CHA

15 +2

Saving Throws DEX +3, CON +9, WIS +5

Damage Resistances Bludgeoning, Piercing, and Slashing from Nonmagical Attacks that aren't Adamantine

Senses Darkvision

Languages Draconic

Challenge 12

Actions

Multiattack. The wyrm makes three attacks: one with its bite, one with its horn, and one with its tail. While burrowing, it cannot use its tail attack. Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one creature. Hit: 13 (2d6 + 6) piercing damage. Horn. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 11 (2d4 + 6) piercing damage. Tail. Melee Weapon Attack: +10 to hit, reach 10 ft., one creature. Hit: 15 (2d8 + 6) bludgeoning damage. Crystal Breath (Recharge 6). The wyrm exhales a beam of light in an 60-foot line that is 5 feet wide. Each creature in that line must make a DC 17 Constitution saving throw, taking 55 (10d10) force damage on a failed save, or half as much damage on a successful one. The ground in the effected area becomes difficult terrain.

A huge white dragon with small crystals all around and on its body.