Cthulhu in GURPS 4e

[Johnny1A.2]

Originally Posted by Anth

In CoC you lose SAN when you are using magic/psionics. There is no SAN roll involved - you just lose SAN.
The human mind is not supposed to handle magic/psionics so therefore you lose your sanity by using them.
I haven't found a good way to emulate this in GURPS yet.

Maybe:

Possessing psi/magic in itself means an automatic -1 penalty on all fright checks, sanity checks, or anything along those lines. Maybe the emergence/first use of a psi power or magical abtility (more or less the same thing in the mythos) automatically gives you some negative quirks, too.

After that, the GM could require that anytime the psi/mage uses his ability more than, say, once in a week, he has to roll against Will or gain some new negative quirk, or a delusion or phobia on a major failure, with higher penalties for 'big' uses, or unusual circumstances.

Over time, the character is either going to learn to be very careful with and sparing of his ability, or he's going to end up as a nutcase, a walking bundle of bizarre and contradictory phobias and disads.