yeah the way Animus magic works makes no sense, I feel like she didn't really go into how casting spells makes one evil. maybe I don't remember but is it just the temptation that they get to do evil? And with Stonemover well I don't think he understood Animus magic well enough. So if its just temptation or a mentality his enchantment wouldn't "redirect the curse to his scales" it just wouldn't work. I think him turning himself to stone has nothing to do with his Animus "evilness" and he basically did that to feel better.