By the end of game you have over 600 AP it is glitched when saying that you only have 425 AP. At almost 80 MP5 you can run your Glacial storm over long periods of team fights, while owning nearly 4K Mana. If you feel like it you can swap out the Zhonya's with Will of the Ancients. You would have 25% spell vamp your ult would do 300 damage and you would constantly heal for nearly 100 as if you were Mundo. With the runes you would rarely find yourself out of mana until you get your Glacial storm level 6. By then you would be coming up on your tear of goddess/ RoA. While chilled your frostbite would do over 1200 damage end game.