Yeah, there's about three or four seconds of freeze immunity that the brother gets after he is done being frozen, that's why example vids show the mage guy taking a break across the coffin. As far as I know, your spells do become more accurate as you level mage. That would explain why a lv 1 mage mostly splashes on white knights while a lv 50+ mage almost doesn't. (yup, tested, not purposely though)