Armor Class: 15 (natural armor)
Hit Points: 130 (17d8 + 51)
Speed: 30 ft.

STR: 11 (+0)
DEX: 14 (+2)
CON: 16 (+3)
INT: 19 (+4)
WIS: 17 (+3)
CHA: 17 (+3)

Saving Throws: INT +7, WIS +6, CHA +6
Skills: Arcana +12, History +12, Perception +9
Damage Resistances: Cold; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks that aren't Silvered
Damage Immunities: Fire, Poison
Condition Immunities: Frightened
Senses: Darkvision 120 ft., passive Perception 19
Languages: Common, Deep Speech, Infernal, Telepathy 120 ft.

Infernal Powers:

• Infernal Flame: Xanatharix can cast fireball as a 5th-level spell once per day, representing his infernal enhancement. The flame appears black and absorbs light.
• Hellish Command: Once per day, Xanatharix can summon 1d4+1 Lemures or 1 Bearded Devil to fight alongside him for up to 1 hour or until they are dismissed or slain. Summoned creatures disappear when the spell ends.

Spellcasting:
Xanatharix is a 17th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 15, +7 to hit with spell attacks). He has the following spells prepared:

• Cantrips (at will): Mage Hand, Prestidigitation, Ray of Frost
• 1st level (4 slots): Detect Magic, Shield, Magic Missile
• 2nd level (3 slots): Darkness, Hold Person
• 3rd level (3 slots): Counterspell, Fireball (in addition to Infernal Flame), Dispel Magic
• 4th level (3 slots): Dimension Door, Black Tentacles
• 5th level (2 slots): Dominate Person, Telekinesis
• 6th level (1 slot): Mass Suggestion
• 7th level (1 slot): Finger of Death

Actions:

• Mind Blast (Recharge 5–6): Emits psychic energy in a 60-foot cone. Each creature in the area must succeed on a DC 15 Intelligence saving throw or take 22 (5d8) psychic damage and be stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with success ending the effect.
• Tentacle Attack: Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 15 (2d10 + 4) psychic damage. If the target is Medium or smaller, it is grappled (escape DC 15) and must succeed on a DC 15 INT saving throw or be stunned until the grapple ends.

Actions:

• Mind Blast (Recharge 5–6): Emits psychic energy in a 60-foot cone. Each creature in the area must succeed on a DC 15 Intelligence saving throw or take 22 (5d8) psychic damage and be stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, with success ending the effect.
• Tentacle Attack: Melee Weapon Attack: +7 to hit, reach 10 ft., one creature. Hit: 15 (2d10 + 4) psychic damage. If the target is Medium or smaller, it is grappled (escape DC 15) and must succeed on a DC 15 INT saving throw or be stunned until the grapple ends.

Legendary Actions:
Xanatharix can take 2 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. Xanatharix regains spent legendary actions at the start of its turn.

• Cast a Spell (Costs 2 Actions): Xanatharix can cast one of his spells, using the appropriate spell slot.
• Tentacle Attack: Xanatharix makes one tentacle attack.