• Legendary Resistance (3/Day). If Yogg-Saron fails a saving throw, it can choose to succeed instead.

• Magic Resistance. Yogg-Saron has advantage on saving throws against spells and other magical effects.

• Regeneration. Yogg-Saron regains 20 hit points at the start of its turn if it has at least 1 hit point remaining.

• Aura of Madness. At the start of each of Yogg-Saron's turns, each creature within 30 feet of it must succeed on a DC 18 Wisdom saving throw or be affected by short-term madness until the start of Yogg-Saron's next turn.

• Multiattack. Yogg-Saron makes three attacks: one with its bite and two with its tentacles.

• Bite. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 21 (3d8 + 6) piercing damage.

• Tentacle. Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 18 (3d6 + 6) bludgeoning damage, and the target is grappled (escape DC 18). Until this grapple ends, the target is restrained, and Yogg-Saron can't use this tentacle on another target.

• Psychic Scream (Recharge 5–6). Yogg-Saron emits a terrifying psychic wail. Each creature within 60 feet of Yogg-Saron that can hear it must make a DC 18 Wisdom saving throw. On a failed save, a creature takes 36 (8d8) psychic damage and is stunned until the end of its next turn. On a successful save, a creature takes half as much damage and isn't stunned.

• Descent into Madness (Recharge 5–6). Yogg-Saron targets up to four creatures within 60 feet, attempting to pull them into a twisted mental landscape. Each targeted creature must succeed on a DC 19 Wisdom saving throw or be transported to the Mind's Eye, a demiplane reflecting Yogg-Saron's psyche.

  While in the Mind's Eye, affected creatures encounter the following:

  • Psychic Assaults. The environment assaults the intruders' minds. At the start of each of their turns, creatures must make a DC 19 Intelligence saving throw, taking 22 (4d10) psychic damage on a failed save, or half as much on a successful one.

  • Manifested Nightmares. Each creature faces illusory manifestations of their deepest fears. These illusions are harmless but require a DC 19 Wisdom (Insight) check to recognize as unreal. Failure results in the creature being frightened until the end of their next turn.

  • Escape the Mind's Eye. To exit, creatures must focus their willpower. As an action, a creature can make a DC 19 Wisdom (Perception) check to locate a mental portal and a DC 19 Intelligence (Arcana) check to activate it. Success on both checks allows the creature to return to the material plane.

  If a creature remains in the Mind's Eye for more than 3 rounds, they must make a DC 19 Wisdom saving throw at the end of each subsequent turn. On a failure, they gain a level of exhaustion due to the mental strain.

Eldritch Bolt. Yogg-Saron conjures a bolt of eldritch energy and hurls it at a creature it can see within 60 feet. The target must make a DC 19 Dexterity saving throw, taking 18 (4d8) necrotic damage on a failed save, or half as much damage on a successful one.

Spawn Tentacle. Yogg-Saron summons a tentacle at a point within 30 feet that it can see. The tentacle occupies a 5-foot square and has an AC of 15, 30 hit points, and immunity to psychic and poison damage. It acts on Yogg-Saron's initiative count and can make the following attack:

• Tentacle Slam. Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage, and the target is grappled (escape DC 18). Until this grapple ends, the target is restrained.

Eldritch Counter. When Yogg-Saron is targeted by an attack, it can use its reaction to respond based on the attack's nature:

• Melee Attack: The attacker must succeed on a DC 19 Strength saving throw or be pushed 10 feet away and knocked prone by a surge of force.

• Ranged Attack: Yogg-Saron creates a momentary distortion, imposing disadvantage on the attack roll.

Yogg-Saron 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. Yogg-Saron regains spent legendary actions at the start of its turn.

• Detect. Yogg-Saron makes a Wisdom (Perception) check.

• Tentacle Attack. Yogg-Saron makes a tentacle attack.

• Cast Spell (Costs 2 Actions). Yogg-Saron casts a spell from its innate spellcasting list.

Innate Spellcasting

Yogg-Saron's innate spellcasting ability is Charisma (spell save DC 21). It can innately cast the following spells, requiring no material components:

• At will: detect thoughts, major image

• 3/day each: dominate person, phantasmal killer

• 1/day each: weird, feeblemind

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.