heys!
it came up again lately and i still don't really know the answer to that question:
most spells are "just" spellcraft checks which are not vs target defence. does that mean, that only the black dice for the real defence of the target are not applied or does the difficulty modifier not apply too?
for example: a meele attack against a greater deamon will normally have a difficulty modifier of at least 2d, so the player takes 2 challenge for the difficulty and lets say 5 misfortune for the defence of the deamon.
now for the wizard: he casts flameblast, which has a difficulty modifier of 1d itself, but is a "spellcraft only" check. so he will not add the 5 misfortune for the defence, but does he add the 2 challenge for the diffictulty?
always a huge discussion in my group and we never seem to find a satisfying answer in the rulebooks…