Insanity Side-Effects 3: Insanity and the Cthulhu Mythos

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Insanity brought on by non-Mythos stimuli yields no Cthulhu Mythos knowledge. However, each time an investigator reels from Mythos-induced trauma (e.g. seeing a Mythos monster, reading a Mythos tome, being affected by a Mythos spell), they learn more of the Mythos, and this is reflected in the Cthulhu Mythos skill. The first instance of Mythos-related insanity always adds 5 points to the Cthulhu Mythos skill. Further episodes of Mythos-induced insanity (Temporary or Indefinite) each add 1 point to the skill.

''Harvey Walters finds a manuscript in Crowninshield Manor. After comprehending it, he has 3% Cthulhu Mythos skill but lost no Sanity points. When he steps outside, Harvey sees a nightgaunt fly overhead. He goes insane, his mind quailing before the unearthly manifestation. Since this is Harvey's first Mythos-related insanity, his player must add 5 percentiles to Harvey's Cthulhu Mythos skill, raising it to 8%. Harvey's maximum Sanity points drops to 91 (99 minus 8 Cthulhu Mythos skill).''