Argenti

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

Aura of Frost. All creatures beginning their turn within 15 feet of the dragon must make a DC-17 Constitution saving throw, taking 10 (2d10) Cold damage on a failed save or half as much on a successful save. 

Ice Walk. The dragon takes no speed penalty when moving through ice or snow. 

Magic Resistances. The dragon has advantage on saving throws against spells.

Keen Senses. The dragon has a +6 bonus on wisdom (perception) checks to detect hidden creatures. 

Draconic Paranoia. The dragon automatically rolls insight checks at advantage against all creatures who tell it something. This roll is not revealed unless otherwise stated. 

Multiattack. The dragon makes three attacks: One with its bite and two with its Claws. It can replace its Bite attack with a use of Spellcasting to cast Ice Knife or Frost Fingers (2nd Level).

Claw. Melee Attack Roll: +12, reach 10 ft. Hit: 12 (2d6 + 6) Slashing damage. On a hit, Hazell may choose to Grapple the creature rather than dealing the slashing damage. Only up to two creatures may be grappled at once in this way.

Bite. Melee Attack Roll: +12, reach 10 ft. Hit: 20 (2d12 + 6) Piercing damage plus 10 (2d10) Cold damage

Tail. Melee Attack Roll: +12, reach 20 ft. Hit: 16 (2d8 + 8) Bludgeoning damage. If the hit beats a creature’s AC by 8 or more points, the creature must succeed a DC-19 Strength saving throw or be knocked Prone. 

Permafrost Breath (Recharge 6). Constitution Saving Throw: DC 20, each creature in a 60-foot Cone. Failure: 54 (12d8) Cold damage and a creature is hindered by ice formations. Success: Half damage only. A creature who is hindered by ice formations has its speed reduced to 0 until it or another creature uses its action to break the ice. If a creature is reduced to 0 hit points by this attack, they are killed and frozen in ice. A creature frozen in this ice can only be revived by melting the ice prior to revival, or magic such as Greater Restoration to cure the petrification prior to the revival spell. Wish of course works as well.

Enthralling Breath. Wisdom Saving Throw: DC 20, each creature within 60 feet of the dragon. Failure: The target has the Charmed condition for one minute. Success: The target is not Charmed. 

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 21, +13 to hit with spell attacks):

At Will: Detect Magic, Hold Monster, Frost Fingers (2nd Level), Ice Knife, Shapechange (Beast or Humanoid form only, no Temporary Hit Points gained from the spell, and no Concentration or Temporary Hit Points required to maintain the spell) Fire Shield (Chill shield version only, cast at the start of combat), Ice Storm
1/Day Each: Zone of Truth, Otiluke's Freezing Sphere, Wall of Ice

Body Shield. Trigger: A creature attempts to target the dragon with a Ranged attack. Reaction: the dragon throws one grappled creature in the path between the shooter and itself. The attacker must succeed a DC-19 Wisdom saving throw to target the dragon rather than the thrown creature. The thrown creature lands Prone 15 feet away from the dragon

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature’s turn, the dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each of its turns.

Chill. The dragon uses Spellcasting to cast Hold Monster. The dragon can’t take this action again until the start of its next turn.

Hailstorm. The dragon uses Spellcasting to cast Ice Storm. The dragon can’t take this action again until the start of its next turn.

Cold Gale. Constitution Saving Throw: DC 19, each creature in a 60-foot-long, 20-foot-wide Line. Failure: 14 (4d6) Cold damage, and the target is pushed up to 30 feet straight away from the dragon. Success: Half damage only. Failure or Success: The dragon can’t take this action again until the start of its next turn.

Tail Whip. The dragon makes one Tail attack.