Mythos undead resemble generic undead in many ways—mindless or fully intelligent, weak or powerful— but all share in common their domination by a Great Old One (usually the King in Yellow, but others may be involved). They usually take the form of a bloated or withered corpse, typically wrapped in stained bandages or wrappings, exhibiting odd discolorations and mutations. It is common for a Mythos undead to have one of its limbs transformed into a tentacle (which still functions as an arm), their tongue or other organ extended to great length, or other similar distortions.
Each Mythos undead creature is a unique manifestation of undeath, defined primarily by its abilities and nature when it lived. Most Mythos undead are, to one degree or another, insane—and this insanity continues to drive them in their unlife, preventing purposeful altruism or all but the most unlikely acts of kindness. The vast majority of Mythos undead who do not directly serve the Great Old Ones are chaotic evil or chaotic neutral, while those who serve the Great Old Ones themselves tend to share their patron’s alignment exactly.
“Mythos undead” is an acquired template that can be added to any living, corporeal creature. A Mythos undead has the base creature’s statistics and special abilities except as noted here.
Challenge Rating: Base creature’s CR +1.
Alignment: A Mythos undead is always chaotic evil or chaotic neutral, or shares the alignment of the Great Old One it serves (which is almost always one of these two alignments).
Senses: A Mythos undead gains darkvision 60 feet.
Defensive Abilities: A Mythos undead retains all of the base creature’s defensive abilities, but also gains damage reduction 5/—, as its dead flesh is difficult to damage. If the base creature had 11 or more Hit Dice, it instead gains damage reduction 10/—. A Mythos undead gains channel resistance +2, or channel resistance +4 if the base creature had 11 or more Hit Dice. As an undead creature, a Mythos undead gains all of the immunities and defensive abilities granted by the undead type. In addition, Mythos undead gain the following defensive ability.
Unless a Mythos undead’s body is completely destroyed (either by reducing it via damage to a negative hit point total equal to its normal hit point maximum, or via an effect like disintegrate), it rises again after 24 hours have passed. When it rises, it does so with a number of hit points equal to its total Hit Dice. In some cases, even the utter destruction of a Mythos undead’s body is not enough to prevent its mind from seeking out another body to inhabit and raise from the dead. In such cases, special rituals or circumstances unique to that Mythos undead must be performed in order to permanently put the undead down.
Certain alchemical techniques can reanimate recently slain bodies, but while these methods restore the semblance of life to the victim, the passage of death to life always results in insanity.
The insane dead are not Mythos undead—they should be treated as zombies with the fast zombie template. Unlike the typical zombie, the insane dead are not intrinsically evil: their drive to savage and harm the living is one of madness, not organized evil. They are chaotic neutral in alignment and cannot be reasoned with.
In rare cases, when certain alchemical techniques are applied to an exceptionally fresh corpse (or even to whole parts of fresh corpses) who, in life, possessed a singularly powerful and focused mind, the result is in an undead creature that retains its intellect; in such a case, create the creature as a Mythos undead.
Sandy Petersen’s Cthulhu Mythos, © 2017, Petersen Games; Authors: Sandy Petersen, Arthur Petersen, Ian Starcher.