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

Magic Resistance. Yrsillar has Advantage on saving throws against spells and other magical effects.

Necrotic Sensitivity. Yrsillar takes an additional 10 Necrotic damage whenever he takes Necrotic damage.

Multiattack. Yrsillar makes two Claw attacks.

Claw. Melee Attack Roll: +11, reach 10 ft. Hit: 13 (2d6 + 6) Slashing damage plus 9 (2d8) Necrotic damage, and the target's Hit Point Maximum is reduced by the same amount as the Necrotic damage dealt. Yrsillar regains Hit Points equal to the Necrotic damage. A creature reduced to 0 Hit Points by this Necrotic damage dies and becomes a ghast.

Voidwave (1/Day). Yrsillar raises his hands and pushes outward, releasing a stream of negative energy in the form of a wall that is 10-feet tall, 60-feet long, and up to 1 inch thick. The wall moves at 30 feet at the start of each of Yrsillar's turns for one minute, and inanimate objects not being worn or held take 35 (10d6) damage if they are in the path. Creatures instead make a saving throw. Dexterity Saving Throw: DC 14, each creature the wall moves through on a turn. Failure: 36 (8d8) Necrotic damage, and the target is Paralyzed for 1 minute. A Paralyzed creature can repeat the saving throw at the end of each of its turns, ending this effect on a success. Success: Half damage only.

Spellcasting. Yrsillar casts one of the following spells without Material components, using Charisma as the spellcasting ability (spell save DC 15).

At Will: Darkness, Detect Evil and Good, Pyrotechnics, Suggestion, Mage Hand (the hand is Invisible)

3/Day Each: Hallow, Blight, Magic Missile (level 5 version), Wall of Fire

1/Day Each: Divine Word, Symbol, Fire Storm

Legendary Action Uses: 3. Immediately after another creature's turn , Yrsillar can expend a use to take one of the following actions. Yrsillar regains all expended uses at the start of each its turns.

Greater Dispelling. Yrsillar selects one spell of level 5 or lower or another magical effect caused by a creature of CR 15 or lower occurring within 120 feet of himself, and ends it immediately. Otherwise, the creature casting the spell or using the ability must make a DC 15 Constitution saving throw, ending the effect on a failure.

Frightful Presence. Yrsillar uses Spellcasting to cast Fear. Yrsillar can’t take this action again until the start of its next turn.

Avenge. Yrsillar can move up to half his Flying Speed, and he makes one Claw attack.