Ancient Ice Dragon

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.

Multiattack. The dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 4 (1d8) cold damage.

Claw. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage. Target must also make a Constitution saving throw (DC 15) or their movement speed is reduced by 10 feet.

Tail. Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: 21 (3d8 + 6) slashing 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 14 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). The dragon exhales an icy blast in a 60-foot cone. Each creature in that area must make a DC 17 Constitution saving throw, taking 70 (16d8) cold damage on a failed save, or half as much damage on a successful one.

Innate Spellcasting. The dragon’s innate spellcasting ability is Charisma (spell save DC 18). It can innately cast the following spells, requiring no material components:

Ice Storm: (2/Day)

Invisibility: (3/Day)

Wall of Ice: (3/Day)

Shapechange: (2/Day)

The 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 dragon 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.

Ice Shard (Costs 2 Actions). The dragon roars, sending shockwaves throughout the cavern. Each creature outside of 30 feet of the dragon must succeed on a DC 17 Dexterity saving throw or take 18 (3d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.