Ancient White Dragon
Gargantuan dragon, chaotic evil
Armor Class 20 (natural armor)
Hit Points 333 (18d20 + 144)
Speed 40 ft., fly 80 ft., swim 40 ft., climb 20 ft., burrow 40 ft.
str
26 (+8)
dex
10 (+0)
con
26 (+8)
int
10 (+0)
wis
13 (+1)
cha
18 (+4)
Saving Throws Dex +6, Wis +7
Skills Perception +13, Stealth +6
Damage Immunities cold
Senses blindsight 60 ft., darkvision 120 ft., passive Perception 23
Languages Common, Draconic
Challenge 20 (25,000 XP)
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 (4/Day, or 5/Day in Lair). If the dragon fails a saving throw, it can choose to succeed instead.
Actions
Cold Breath. Constitution Saving Throw: DC 22, each creature in a 90-foot Cone. Failure: 63 (14d8) Cold damage. Success: Half damage.
Multiattack. The dragon makes three Rend attacks.
Rend. Melee Attack Roll: +14, reach 15 ft. 17 (2d8 + 8) Slashing damage plus 7 (2d6) Cold damage.
Attack Summary
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 ancient white dragon regains spent legendary actions at the start of its turn.
Freezing Burst. Constitution Saving Throw: DC 20, each creature in a 30-foot-radius Sphere [Area of Effect]|XPHB|Sphere centered on a point the dragon can see within 120 feet. Failure: 14 (4d6) Cold damage, and the target's Speed is 0 until the end of the target's next turn. Failure or Success: The dragon can't take this action again until the start of its next turn.
Frightful Presence. The dragon casts Fear, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 18). The dragon can't take this action again until the start of its next turn.
Pounce. The dragon moves up to half its Speed, and it makes one Rend attack.