[quote=@Sublimation]
A rank magic resistance is exceptionally rare for a reason. Not everyone has the luxury of no selling Casters from the Age of Gods without a second thought. Dragon's Blood/Phantasmal Pedigree is a way of attaining this. The more common way of getting this is by having strong Faith, like Joan of Arc, Saint George, etc.  Christian protections, particularly those regarding saints, grant A rank MR. However without extenuating circumstances, A rank MR should not be possible, and I have no idea where the "cannot go below class specifications" thing comes from when it doesn't apply to parameters and other classes' skills either.
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Yeah, servants can even have negative stats, or 'negated stats'. My assassin will have no class ability because he's an 8 foot tall monstrosity that had D+ rank agility, he ain't hiding nowhere... Unless the room is pitch black, I guess he could blend in there.