Falenas, Lady of The Lake

Legendary Resistance (3/Day, or 4/Day in Lair). If the dragon fails a saving throw, it can choose to succeed instead.

Amphibious. The dragon can breathe air and water.

Oathbound Dominion. Any creature bound by one of the dragon’s oaths is aware of its commands, regardless of distance. (See Oaths below.)

Tainted Frost. A creature that starts its turn within the dragon's Tainted Frost or enters it for the first time takes 7 (2d6) Cold damage. It must also make a *Constitution Saving Throw:* DC 17. *First Failure:* The creature is Restrained and repeats the save at the end of its next turn if it is still Restrained, ending the effect on a success. *Second Failure:* The target is Petrified instead of the Restrained condition. The Petrified condition ends after 1 minute as long as it is not in water.

Multiattack. The dragon makes three Rend attacks. It can replace one attack with a use of (A) Paralyzing Breath or (B) Spellcasting to cast Ice Knife.

Rend. Melee Attack Roll: +13, reach 10 ft. Hit: 17 (2d8 + 8) Slashing damage plus 4 (1d8) Cold damage. If a creature is inside of the dragon's Tainted Frost, it instead takes 18 (4d8) Cold damage.

Cold Breath (Recharge 5–6). Constitution Saving Throw: DC 19, each creature in a 60-foot Cone. Failure: 54 (12d8) Cold damage that makes immunity go to resistance instead. Success: No damage. In addition, the dragon's Tainted Frost flows around it in a 30 ft emanation until the end of the dragon's next turn.

Paralyzing Breath. Constitution Saving Throw: DC 19, each creature in a 60-foot Cone. First Failure: The target has the Incapacitated condition until the end of its next turn, when it repeats the save. Second Failure: The target has the Paralyzed condition, and it repeats the save at the end of each of its turns, ending the effect on itself on a success. After 1 minute, it succeeds automatically.

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 18, +11 to hit with spell attacks):

At Will: Detect Magic, Hold Person, 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)
1/Day Each: Ice Storm (level 5 version), Zone of Truth, Control Water.

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 Person. The dragon can’t take this action again until the start of its next turn.

Cold Gale. Dexterity Saving Throw: DC 19, each creature in a 60-foot-long, 10-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.

Pounce. The dragon moves up to half its Speed, and it makes one Rend attack.