MR & SP

[Graeme Dice]

magnate said:
Alneyan - so for proof against a basic spell penetration of 11 I need MR of 21 or 22, right? (21 if a draw means a save, 22 if a draw means the spell takes effect)

You are never proof against basic spell penetration, as an unlimited number of open ended die rolls are possible.

I presume that the bonus for high paths is +1 per path level higher than needed to cast the spell.

+1 per 2 levels higher than needed.

I know it's not exactly proof because of the open-ended rolls, but apart from that possibility (which you can never eliminate altogether), MR of 21 or 22 should be enough for most things ...?

21 or 22 puts the probability of failure down to somewhere in the neighbourhood of 1%. As such, you are probably going to lose it eventually to a dedicated mage squad that carries spell foci.