Cassis, The Unspoken One

 Trait: Magic Resistance

Text:
Cassis has advantage on saving throws against spells and other magical effects.

Trait: Master of Stolen Names 

Text:
Creatures of Cassis’s choice within 30 feet of him have disadvantage on saving throws to maintain concentration. A creature that fails a concentration check within this aura takes 7 (2d6) psychic damage.

Cassis is a 20th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 21, +13 to hit with spell attacks).

Cantrips (at will): mage hand, minor illusion, ray of frost, shocking grasp, toll the dead
1st level (4 slots): shield, absorb elements, detect magic, disguise self, silvery barbs
2nd level (3 slots): misty step, mirror image, invisibility, hold person
3rd level (3 slots): counterspell, dispel magic, fireball, hypnotic pattern
4th level (3 slots): greater invisibility, dimension door, blight
5th level (3 slots): dominate person, wall of force, synaptic static
6th level (2 slots): disintegrate, globe of invulnerability
7th level (2 slots): forcecage, finger of death
8th level (1 slot): maze, mind blank
9th level (1 slot): power word kill

Trait: Spell Thief

Text:
When a creature Cassis can see within 60 feet casts a spell of 6th level or lower, Cassis can force that creature to make an Intelligence saving throw (DC 21) as a reaction. On a failed save, the spell fails, has no effect, and Cassis steals the spell’s pattern until the end of his next turn. Until then, Cassis can cast that spell once without expending a spell slot, using his spellcasting ability.
Cassis can steal only one spell at a time. If he steals a new spell, the previous stolen spell is lost. This functions as counterspell. Cassis Starts encounters with the following stolen spell -- Mental Prison:

You attempt to bind a creature within an illusory cell that only it perceives. One creature you can see within range must make an Intelligence saving throw. The target succeeds automatically if it is immune to being charmed. On a successful save, the target takes 5d10 psychic damage, and the spell ends. On a failed save, the target takes 5d10 psychic damage, and you make the area immediately around the target’s space appear dangerous to it in some way. You might cause the target to perceive itself as being surrounded by fire, floating razors, or hideous maws filled with dripping teeth. Whatever form the illusion takes, the target can’t see or hear anything beyond it and is restrained for the spell’s duration. If the target is moved out of the illusion, makes a melee attack through it, or reaches any part of its body through it, the target takes 10d10 psychic damage, and the spell ends.

Action: Multiattack

Text:
Cassis makes three attacks with Whisperknife or casts one spell and makes one Whisperknife attack. Or, he makes a specialty attack and casts one spell or makes one attack.

Action: Whisperknife (Magic Dagger)

Type: Melee or Ranged Weapon Attack
To Hit: +13
Reach/Range: 5 ft. or range 20/60 ft.
Target: one creature
Hit: 10 (1d4 + 8) piercing damage plus 14 (4d6) necrotic damage.
If Cassis can apply Sneak Attack, the target takes an extra 28 (8d6) psychic or necrotic damage (Cassis’s choice).

Action: Hand of the Whispered One (Recharge 5–6)

Text:
Cassis unleashes corrupt force through the Hand of Vecna. Each creature of Cassis’s choice within 30 feet must make a DC 21 Constitution saving throw, taking 45 (10d8) necrotic damage on a failed save, or half as much damage on a successful one.
A creature that fails this save can’t regain hit points until the end of Cassis’s next turn.

Action: Eye-Ray of Unmaking (Recharge 6)

Text:
Cassis targets one creature he can see within 120 feet. The target must make a DC 21 Dexterity saving throw, taking 54 (12d8) force damage on a failed save, or half as much on a successful one.
If the target is reduced to 0 hit points by this damage, its body begins to crumble into gray ash and cannot be restored except by true resurrection, wish, or similarly powerful magic.

Action: Steal Memory (1/Day or 3/Day)

Text:
Cassis targets one creature he can see within 60 feet. The target must succeed on a DC 21 Intelligence saving throw or take 27 (6d8) psychic damage and be memory-riven until the end of Cassis’s next turn. While memory-riven, the creature:

• can’t take reactions,

• has disadvantage on attack rolls and ability checks, and

• if it casts a spell, it must first succeed on a DC 21 spellcasting ability check or the spell is wasted.

Bonus Action: Vile Teleport 

Text: Cassis teleports, along with any equipment he is wearing or carrying, up to 30 feet to an unoccupied space he can see. He can cause each creature of his choice within 15 feet of his destination space to take 10 (3d6) psychic damage. If at least one creature takes this damage, Cassis regains 30 hit points.

Bonus Action: Cunning Action

Text:
Cassis takes the Dash, Disengage, or Hide action.

Cassis has two reactions but can only take one during their turn.

Reaction: Spell Thief 

Text:
When a creature Cassis can see within 60 feet casts a spell of 6th level or lower, Cassis can force that creature to make a DC 21 Intelligence saving throw. On a failed save, the spell fails, has no effect, and Cassis steals it until the end of his next turn (see Spell Thief trait).

Reaction: Uncanny Dodge

Text:
When an attacker Cassis can see hits him with an attack, Cassis halves the attack’s damage against him.

Text:
Cassis 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. Cassis regains spent legendary actions at the start of his turn.

Legendary Action: Whisperknife Attack

Cost: 1
Text:
Cassis makes one Whisperknife attack.

Legendary Action: Save Face

Cost: 1
Text:
Cassis twists memory and perception to deny a moment of weakness. Cassis either moves up to 20 feet without provoking opportunity attacks and becomes lightly obscured by illusory afterimages until the start of his next turn. While obscured this way, the next attack roll made against him before the start of his next turn is made with disadvantage.

Legendary Action: Cast a Spell (3rd Level or Lower)

Cost: 1
Text:
Cassis casts a prepared spell of 3rd level or lower.

Legendary Action: All the Secrets

Cost: 1
Text:
Cassis tears hidden truths from the minds of his enemies. Cassis chooses one creature he can see within 60 feet. Cassis learns whether the creature has any damage resistances, immunities, or condition immunities, and one spell it has prepared or can cast (DM’s choice if multiple are available). Then choose one of the following effects:

• Expose Weakness. The next attack roll made against that creature before the end of Cassis’s next turn has advantage.

• Stolen Timing. The creature has disadvantage on the next saving throw it makes before the end of Cassis’s next turn.

• Fracture Concentration. If the creature is concentrating, it immediately makes a concentration check (DC 17).

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.