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.
Sion, going almost pure AP - Enrage first, so you can farm last hits and gain some hit points. Then, split Early on between your gaze and caress to keep the mana costs under control, take cannibalism at 6, then max out both gaze and caress before you pick up the next rank in cannibalism. Finish off enrage and Cannibalism, and enjoy.