Legendary Resistance (3/Day). If Strahd fails a saving throw, he can choose to succeed instead.

Spellcasting. Strahd is a 9th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 20, +14 to hit with spell attacks). Strahd has the following Wizard spells prepared:
Cantrips (at will): Mage Hand, Ray of Frost, Chill Touch

1st level (7 slots): Fog Cloud, Sleep, Charm Person, Ray of Sickness

2nd Level (6 slots): Detect Thoughts, Gust of Wind, Mirror Image, Blindness/Deafness, Flaming Sphere

3rd Level (5 slots): Animate Dead, Fireball, Nondetection, Counterspell, Vampiric Touch 

4th Level (4 slots): Blight, Greater Invisibility, Polymorph, Confusion, Hallucinatory Terrain, Ice Storm, Wall of FIre

5th Level (3 slots): Animate Object, Scrying, Cloudkill, Immolation

6th Level (3 slots): Chain Lighting, Eyebite, Disintegrate, Mass Suggestion, Otto's Irresitibile Dance

7th Level (2 slots): Finger of Death, Forcecage, Power Word Pain, Mirage Arcana

8th Level (1 slots): Feeblemind, Power Word Stun

9th Level (1 slots): Forsight, Meteor Swarm, Power Word Kill, Time Stop

Shapechange: Strahd can change shape back into his original humanoid shape from when he was alive in Barovia, however, the dragon is his true form and he cannot attack or use spells other than charm person, mass suggestion, and mirage arcana when in his humanoid form. 

Spider Climb: Strahd can climb difficult surfaces including upside down on ceilings without having to make an ability check in either humanoid or dragon form. 

Opening Attack: Case spell "Insanity" all players roll an intelligence check, on a failed 18 save, gain one d100 insanity effect. 

Multiattack: Strahd can make three attacks: one with its bite attack and two with its claw attack. 

Bite: Melee Weapon Attack: +14 to hit, reach 10 ft, one target. Hit: 19 (2d10 + 8) piercing damage plus 7 (2d6) necrotic damage. 

Claw: Melee Weapon Attack: +14 to hit, reach 5 ft, one target. Hit 15 (2d8 + 8) bludgeoning damage. 

Tail: Melee Weapon Attack: +14 to hit, reach 15 ft, one target. Hit: 17 (2d8 + 8) bludgeoning damage. 

Frightful Presence: Each creature of the dragon's choice that is within 120 feet of the dragon and aware of it must succeed a DC 19 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. 

Bloodfire Breath (Recharge 5-6). Strahd exhales blood fire in a 60 foot cone. Each creature in that area must make a DC 21 Dexterity saving throw, taking 63 (18d6) fire damage on a failed save or half on a successful one. On a failed save, the creature is stricken with a Blood Curse and covered in burning blood for 3 rounds. Each time the affected creature is hit with a melee attack by Strahd they take an additional 2d12 damage that is unaffected by resistances or immunities and the damage they take heals Strahd. 

Strahd 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. Strahd regains spent legendary actions at the start of his turn. 

Detect: Strahd makes a Wisdom (Perception) check.

Wing Attack (Cost 2 Action): Strahd beats his wings. Each creature within 10 feet must succeed on a DC 20 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. Strahd can then fly up to half his flying speed.

Wound (Costs 3 Actions): Strahd curses a creature of his choice that he can see. The creature must make a DC18 Constitution saving throw or they take 1d12 necrotic damage and are stunned until the end of their next turn.