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Yithian, Past

The creature resembles a mollusk with an iridescent, vaguely cone-shaped body about ten feet tall and a wide, snail-like foot. Four protrusions sprout from the dorsal side of the body: two claws, a grasping mouth, and a horrific head bristling with sensing tentacles.

Large aberration, lawful neutral

Armor Class 16 (natural armor)

Hit Points 126 (12d10 + 60)

Speed 20 ft., climb 10 ft.

25 (+7 16 (+3) 20 (+5 23 (+6 17 (+3) 17 (+3)

Saving Throws Con +9, Int +10, Wis +7, Cha +7

Skills Arcana +10, History +14, Insight +7, Nature +10, Persuasion +7, Yog-Sothothery +11

Damage Resistances acid, fire; bludgeoning, piercing, and slashing from nonmagical attacks

Senses blindsight 60 ft., darkvision 60 ft., passive Perception 13

Languages Aklo, Yithian, any 10 other languages, telepathy 100 ft.

Challenge 11 (7,200 XP)

Special Traits

  • Innate Spellcasting (Psionics). The yithian’s spellcasting ability is Intelligence (spell save DC 18). It can innately cast the following spells, requiring no components:
    • At will: detect thoughts, hold monster, modify memory
    • 1/day: astral projection (self only)
  • Keen Sight. The past yithian has advantage on Wisdom (Perception) checks that rely on sight.


  • Multiattack. The past yithian makes either two pincer attacks or two lightning gun attacks.
  • Pincer. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 20 (3d8 + 7) bludgeoning damage. If the yithian scores a critical hit, it rolls damage dice three times, instead of twice.
  • Lightning Gun (6/day). Ranged Spell Attack: +10 to hit, range 150/600 ft., one target. Hit: 22 (3d10 + 6) lightning damage.
  • Amnesia (Recharge 5–6). The yithian attempts to erase the memories of a creature it can communicate with telepathically. The target must make a DC 18 Intelligence saving throw. On a failure, it loses all memories except those the yithian chooses to leave intact and the yithian can choose to deal 82 (15d10) psychic damage to it. While amnesiac, the target can’t apply its proficiency bonus on ability checks or Intelligence or Wisdom saving throws. A remove curse or greater restoration spell or similar magic cast on the target restores lost memories. If your game uses insanity and dread (see chapter 4), treat this as an insanity. A creature that succeeds on its saving throw against this effect takes half as much psychic damage and can’t have its memory erased by Amnesia for 24 hours (although it still takes psychic damage if targeted again during that time).
  • Mind Swap. The yithian attempts to exchange minds with a creature it can communicate with telepathically. The target must make a DC 16 Charisma saving throw or be possessed by the yithian. On a failed save, the yithian’s soul moves into the target’s body and the target’s soul moves into the yithian’s body. On a successful save, the target is unaffected and becomes immune to that yithian’s Mind Swap for 24 hours. Once the yithian swaps minds with a creature, it takes complete control of that creature’s body. The yithian’s game statistics are replaced by the target’s, though the yithian retains its alignment and its Intelligence, Wisdom, and Charisma scores. The yithian keeps its Innate Spellcasting trait and its Amnesia and Mind Swap. The yithian can’t use the target’s class features. Meanwhile, the target gains the yithian’s statistics except for alignment and Intelligence, Wisdom, and Charisma scores. The target retains the use of class features compatible with the yithian’s physical form but can’t use the yithian’s Innate Spellcasting trait, Amnesia, or Mind Swap. The target’s ability to use the yithian’s equipment might be limited (for example, the lightning gun’s rules on page 126 limit how a non-yithian target can use it). While the yithian controls another creature’s body, it can use its action to reverse the effect at any range, instantly returning both minds to the proper bodies. If the yithian wishes, it can use its Amnesia action on the creature as a bonus action immediately after reversing the swap. If a possessed body dies, its possessing mind dies with it and the other body permanently retains its possessing mind. Casting dispel magic (treat this as a 6th-level spell) or remove curse on either creature with a swapped mind causes each of the two swapped minds to return to its previous body unless either body is dead. Reviving a body that died while possessed by a swapped mind causes that original mind to return to the revived body, which kills the body left mindless.


Yithians are massive—typically standing over 10 feet tall and weighing 4 or more tons—and very long-lived. An individual yithian can evade death by mind-switching with another creature. If a yithian’s body is killed before it can switch minds, it does indeed die.

Section 15: Copyright Notice

Sandy Petersen’s Cthulhu Mythos, © 2018, Petersen Games; Authors: Sandy Petersen, David N. Ross, James Jacobs, Arthur Petersen, Ian Starcher.