So, a mentor spirit can give you +2 DP to spell-X tests. Is that just for the casting roll, or does that count to drain tests for those spells as well? I couldn't find anything on it in the mentor spirit rules.

I'd be happy to give the bonus to both. Is that particularly broken, do you think?

just the casting roll. I think it gets overpowered if you give it to drain as well.

I'm kind of on the fence, because drain is the drawback of magic and making drain easier makes magic easier. Also, for spellcasting, considering that the DP for slinging spells decreases based on visibility modifiers those extra dice are more often than not going to be offsetting penalties. All in all, I'm leaning more toward the no...especially after my GM let me purchase the hits for drain tests. Another 2 DP in drain resistance and I'm buying off the drain of a Force 9 Stunbolt...which is just broken.

pretty sure someone asked one of the developers this question recently, and they said it was not intended to affect the drain roll.