Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
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