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.
i have tried this build for Sion for some games and it seems to work for me.
i use cryptic gaze's stun as first skill,for safety reasons and hunting/fighting.
early enrage in lvl2, is for survivability reasons(it's like wearing a warmog's armor)and of course dmg,which helps farming.
after i just lvl with death's caress,which offers me lots of dps,even i need it to kill or farm.
cryptic gaze+death's caress+some hits,when required +ulty,is a very simple way to kill and thats what i like on Sion.