Ancient White Dragon

Gargantuan dragon · CR 20

Armor Class 20

Hit Points 333 (18d20+144)

Speed burrow 40 ft., fly 80 ft., swim 40 ft., 40 ft.

STR 26 +8

DEX 10 +0

CON 26 +8

INT 10 +0

WIS 13 +1

CHA 14 +2

Saving Throws CHA+8, CON+14, DEX+6, WIS+7

Skills perception +13, stealth +6

Damage Immunities cold

Senses blindsight60 ft., darkvision120 ft. , passive Perception 23

Languages Common, Draconic

Traits

Ice Walk.: The dragon can move across and climb icy surfaces without needing to make an ability check. Additionally, difficult terrain composed of ice or snow doesn't cost it extra movement.
Legendary Resistance (3/Day).: If the dragon fails a saving throw, it can choose to succeed instead.

Actions

Multiattack.: The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.
Bite. Melee/Ranged Weapon Attack: +14 to hit.: Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 9 (2d8) cold damage.
Claw. Melee/Ranged Weapon Attack: +14 to hit.: Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 15 (2d6 + 8) slashing damage.
Tail. Melee/Ranged Weapon Attack: +14 to hit.: Melee Weapon Attack: +14 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.
Frightful Presence.: Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 16 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.
Cold Breath (Recharge 5-6). Melee/Ranged Weapon Attack: +0 to hit.: The dragon exhales an icy blast in a 90-foot cone. Each creature in that area must make a DC 22 Constitution saving throw, taking 72 (16d8) cold damage on a failed save, or half as much damage on a successful one.

Legendary Actions

The Ancient White Dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The creature regains spent legendary actions at the start of its turn.

Detect.: The dragon makes a Wisdom (Perception) check.
Tail Attack.: The dragon makes a tail attack.
Wing Attack (Costs 2 Actions) (Costs 2 Actions).: The dragon beats its wings. Each creature within 15 ft. of the dragon must succeed on a DC 22 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.