Give kassadin magic resist per level.
Well, his passive is reduce 15% magic damage right? but if your magic resist still stay at 30 till level 18, i dont feel like kassadin is a champion who can really take magic damage. And he is an assasin have ap ratio 200% (compare to other ap assasin, this ratio is really like shit, and he have to build mana first cuz he didnt have so much mana early game, so i think give him magic resist late game is fine.)