Alastor

Legendary Resistance (3/day). If the Alastor fails a saving throw, it can choose to succeed instead

Devil's Sight. Magical darkness doesn't impede the Alastor's darkvision.

Innate Spellcasting. Alastor's innate spellcasting ability is Charisma (spell save DC 23, +15 to hit with spell attacks). It can innately cast the following spells, requiring no material components:

At will: vicious mockery (4d4 damage), command, dissonant whispers, tasha's hideous laughter

3/day each: hunger of hadar, summon shadowspawn, dispel magic, fear

1/day each: evard's black tentacles, shadow of moil, synaptic static, enervation

Unleash True Self. Alastor reveals his terrifying form. All creatures of his choice within 120 feet must succeed on a DC 23 Wisdom saving throw. On a failure they are frightened of him 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.

In addition he gains the following benefits:

He gains resistance to all damage types except radiant. If he already had resistance he gains immunity.

He gains advantage on saving throws against spells and other magical effects.

His lair actions summon double the number of darkness areas or shadows.

As part of his multiattack he can now cast spells of his 3/day options.

The transformation lasts for 1 minute and Alastor can end it at will.

Multiattack. Alastor makes two Shadow Tendril attacks and casts one of his at will spells. He can't cast the same spell two rounds in a row

Shadow Tendril. Melee Spell Attack: +15 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) necrotic damage and 17 (2d8 + 8) piercing damage. When both the target of the attack and Alastor are in darkness the reach of this attack is increased by 10 feet and it deals an additional 1d8 of each damage type.

Shadow Blend. While in darkness, Alastor can Hide as a bonus action, even while being observed.

Sinister Satire. Alastor taunts all creatures within 60 feet. All creatures who can hear him are affected as if by the Vicious Mocker cantrip.

Absorb Shadows. Alastor absorbs the shadows of a darkness spell he is within range of to replenish his strength. The darkness dissipates and he regains 20 hit points. If Alastor received radiant damage since the end of his last turn he only restores 10 hit points

Disperse into Shadow. When Alastor is hit with an attack, he can halve the attack's damage against him and teleport up to 60 feet to an unoccuoled area

Disperse into Shadow. Alastor 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. He regains spent legendary actions at the start of its turn

Attack. Alastor makes one Shadow Tendril attack

Shadow Step. Alastor teleports up 150 feet to an area of darkness.

Cast a Spell (Costs 2 Actions). Alastor uses Spellcasting.

Mythic Action Name. Enter the description for how mythic actions work for your monster here.

Mythic Action Name (Costs # Actions). Enter the description for your mythic action.