Alicia Ravenof

Magic Resistance. Alicia has advantage on saving throws against spells and other magical effects.

Unholy Rebirth (1/day). If Alicia would be reduced to half of her hit points or fewer,
encases herself in a cocoon of blood and shadow that grants her 300 temporary hit points and incapacitates her until the end of her next turn. If the cocoon is destroyed before completing its process, Alicia receives a -2 penalty to her AC for the rest of the encounter. If the cocoon terminates the process, Alicia regains 5d10 hit points and can use mythic actions.

Legendary Resistance (3/day). If Alicia fails a saving throw she can decide to succeed instead.

Profane Edge. Alicia's weapon attacks deal an additional 24 (5d8) necrotic damage on a hit.

Aura of Sanguine Restitution. Each creature that begins its turn within 20 feet of Alicia or enters her aura for the first time in a turn must make a DC19 Constitution saving throw; on a failed save the creature takes 3d8 necrotic damage and Alicia is healed for half that amount.

Spellcasting. [Alicia] is a 18-level spellcaster. Her spellcasting ability is [Charisma] (spell save DC 20, +12 to hit with spell attacks). [Alicia] has following spells prepared:
Cantrips (at will): [guidance], [sacred flame] 
1st level (4 slots): [command], [compelled duel], [searing smite]
2nd level (3 slots): [hold person], [magic weapon], [vampiric touch]
3rd level (3 slots): [dispel magic], [elemental weapon], [animate undead], [summon undead]
4th level (3 slots): [banishment], [staggering smite], [spirit of death]
5th level (2 slots): [destructive wave] (necrotic), [banishing smite]

Multiattack. Alicia can take 2 atacks using her claymore and then she can cast a spell of 3rd level or lower as a bonus action or use her Spectral Spear if available. Alicia can replace one attack for a Crimson Fangs attack.

Vampiric Fangs. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 16 (2d6 + 7) [piercing] damage + (4d6) [necrotic] damage and Alicia is healed by the total amount of necrotic damage delt with this attack.

Crimson Claymore. MeleeWeapon Attack: +15 to hit, reach 5 ft., one target. Hit: 40 (1d12 + 9) [slashing] damage + (5d8) [necrotic] damage.

Dreadful Aspect (Recharges after a Short or Long Rest). Each enemy within 30 feet of Alicia must succeed on a DC 19 Wisdom saving throw or be frightened of her for 1 minute. If a frightened target ends its turn more than 30 feet away from Alicia, the target can repeat the saving throw, ending the effect on itself on a success.

Nightsinger's Spectral Spear (Recharge 5-6). Alice conjures a phantasmal spear of shadows in her open hand and throw it whirling through the air. The spear travels in a 60-foot long, 10-foot wide line, coming to rest hovering in the air at the end of its line or before it strikes any solid objects. Each creature within the area while the spear is moving must make a Dexterity saving throw or take 8d8 necrotic damage, or half as much on a successful save. A creature has disadvantage on this saving throw if the spear comes to rest in the creature's space. If Alicia is within 120 feet of the spear at the start of her next turn, it returns to her in a 10-foot wide line, forcing creatures within its area of travel to make saving throws against the spear's damage.

Enter the description for how bonus actions work for your monster here.

Power Word: Silentum. When a creature Alicia can see within 60 feet of her begins to cast a spell with verbal components she can raise a negation word and force the creature to make a DC19 Charisma saving throw or be silenced until the end of its turn. A silenced creature cannot speak or cast spells that require verbal components.

Power Word: Fortificare. If Alicia is hit by an attack from a creature she can see, she can use her reaction to gain resistance against that type of damage until the end of the current turn.

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

Claymore Attack (Costs 1 Action). Alicia makes a weapon attack.

Move (Costs 1 Action). Alicia moves up to half her speed.

No Rest for the Wicked (Costs 3 Actions). Alicia revitalizes one undead creature under her command and revives it with half its hit points.

Command the Fatihless (Costs 2 Actions). Alicia casts the command spell as a 3rd level spell without using any spell slot.

Cast a Spell (Costs 2 Actions). Alicia casts a spell from her list of prepared spells, using a spell slot as normal.

As an action Alice can use her Hellfire Orb once per day after her Unholy Rebirth.

Hellfire Orb (1/Day). Alicia hurls a magical ball of fire that explodes at a point it can see within 120 feet of it. Each creature in a 20-foot-radius sphere centered on that point must make a DC 19 Dexterity saving throw. The sphere spreads around corners. A creature takes 35 (10d6) fire damage and 35 (10d6) necrotic damage on a failed save, or half as much damage on a successful one.