Argynvost the Dracolich

Legendary Resistance (3/Day

Magic Resistance: Advantage on saving throws against spells and other magic effects. 

Spell-casting:  Argynvost is a 7th level spell-caster, using charisma as is spell casting ability.  Its spell attack bonus is +10, and its spell save DC is 18.  He knows the following spells and the corresponding number of spell slots. 

Level 1 spells (4 slots): thunderous smite, Divine favor (dealing necrotic damage), Hellish rebuke (dealing cold damage), hex

Level 2 spells (2 slots): Darkness, [spell][Spiritual weapon/spell]

Dracosmite.  Once per round, when Argynvost hits with a claw attack, he can empower it with energy granted by the dark powers. By spending one spell slot, he empowers his claw attack with necrotic energy, dealing 2d8 extra necrotic damage. The damage increases by 1d8 if he uses a level 2 slot. 

Multiattack: Argynvost can use his frightful presence. He can then make 2 attacks, 1 with claw and one with bite. 

Bite. Melee Weapon Attack: +13 to hit, reach 10 ft., one target. Hit: 19 (2d10 + 8) piercing damage.

Claw. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 15 (2d6 + 8) slashing damage.

Frightful Presence. Each creature of Argynvost's choice that is within 120 feet  aware of him must succeed on a DC 18 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 Argynvost's Frightful Presence for the next 24 hours.

Breath Weapons (Recharge 5-6): The dragon uses one of the following breath weapons.
Cold Breath. The dragon exhales an icy blast in a 60-foot cone. Each creature in that area must make a DC 20 Constitution saving throw, taking 45 (10d8) cold damage on a failed save, or half as much damage on a successful one.
Paralyzing Breath. The dragon exhales paralyzing gas in a 60-foot cone. Each creature in that area must succeed on a DC 20 Constitution saving throw or be Paralyzed 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.

Argynvost can take 3 legendary actions, choosing from the options below. Only one legendary option can be used at a time, and only at the end of another creature's turn. Argynvost regains legendary actions at the start of his turn.

Armor of Agathys: Argynvost Casts Armor of Agathys at 2nd level without using a spell slot. 
Wing Attack (Costs 2 Actions): Argynvost beats its wings. Each creature within 10 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. 

Claw Attack: Argynvost makes a claw attack.