Question about mythos magic

[MarvelousMrMean]

I am relatively new to CoC and have a quick question about mythos magic. If an investigator uses the spell shrivelling and invest 10 magic points plus 5 san, does this make the investigator have a bout of madness since it is a loss of 5 san at one moment?

[Israeldor]

After losing 5 sanity in one go the player character needs to make an intelligence roll. If failed nothing further happens. If passed they go temporarily insane, see bout of madness & underlying insanity. Applicable pages are keeper guide pages 155-159.

[MarvelousMrMean]

Thank you for the clarification of the ruling.

[EricW]

I think its important to consider giving the magic a cost which goes beyond a bit of SAN accounting. Most of the Cthulhu stories the magic had side effects, attracted the attention of otherworldly beings or stirred up forces the wizard didn't want or wasn't aware of. For example after using shrivelling (yikes!) your PC might have a horrible episode where they fail asleep and wake up next to a shrivelled corpse, apparently after sleep walking and doing something unspeakable with no conscious recollection of what they did. Of course its up to you to decide if the PC was actually responsible for the corpse. Or they might have nightmares about their loved ones shrivelling up. Or maybe find someone's severed finger in their sock drawer.

Edited October 14, 2020 by EricW