Not Updated For Current Season
This build is based on an awesome ability of soraka's, starcall, this ability at rank 1 reduces magic resist by 8. This debuff can be cast every 3 seconds(average) and stacks 20 times. yes if u can cast it enough -180 magic resist. but because no one wants to fight for 1 minute just be useful i have added abyssal scepter and malady for a quick 44 more to this. SO if someone is standing close to u you remove 20 MR and with 1 starcall and autoattack and additional 14. withing 3 seconds should have 4 malady, 2 starcall, and 1 abyssal aura debuff on your target reducing MR by 60.. this is enough to take any monster/minion(excluding baron) into the negatives increasing the magic damage taken. Exhaust mastery also adds an additional -10 MR to exhaust.
I have found that this build has low hp and armor. so filling in the last 2 items with this might be advises.
Build also works well on AP evelynn, Fiddlesticks, and Morgana... they also have MR redction abilities