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 entirely on ability power. You have to buy mejai's soulstealer in early game. If you do soon get a lead on ability power. You also need anyway Rylai Cristal's Sceptre and Rabandon's. Rylai Cristal's Sceptre is useful because it can slow people so you can easily use Call of the void on them. Rabandon Deathcap's gives you a lot of ability power. These are the items that you should have anyway. I hope you find it useful.