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.
Basically this is what I use. Just felt its worth the add.
Basically it excels at simple damage through means of magic for 1-2 enemy champions and attack damage in team fights. The extra armour here and there is for survivability including the hp from his passive.
P.S THE LAST ITEM IS CONDITIONAL. Use some initiative and boost your AP Damage or Survivability:) stack another TE or gunblade if you like!