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.
Summoner spell explanation:
Ghost is for chasing down those fast buggers trying to run away eventually saving or building up your stacks.
Clarity is the most confusing, pantheon is very mana hungry throughout the game, and it's not worth it to buy any different items to fix that costing your valuable, valuable inventory slots.
1.) This item is only for those who know how to effectively use pantheon in every situation; a master's only item, it is what will make or break this strategy. Utilize your jumps perfectly and you will love this item forever, don't and well... get a different item.
2.) Pantheon is not always able to finish off his opponents right after his combo, so it is important to be able to have some attack speed along with all of his attack damage, making him strong even without his skills.
3.) The reason I buy blood thirsterers first before the infinity edge is because with it, you will not only have the damage it gives, but the life steal is the prime reason. If you are hurt after a team battle or before, you will be able to heal very quickly on minions or passive jungle monsters and it will get you back in the fight that much quicker.
4.) Infinity edge is to boost your attack damage as well as to increase your heart seeker's special ability which is to critically hit every hit with heartseeker while under 15% health. The extra critical chance will also help you if your stun to heartseeker fails, because you will obviously have to start auto attacking.
5.) Last whisper is to boost your attack speed and to mainly break through armor. It will allow you to start not even needing to use your skills to kill someone because your auto attack damage will be hitting like a truck.
6.) This is for the same reason for buying the first.
Sword of the occult - Phage, and to frozen mallet after infinity edge.
Last blood thirsterer - Black Cleaver for armor teams.
Start off by buying a long sword and a health potion. This allows you to be able to deal some decent damage early game. Use your Spear Shot often to last hit and to harass. You should attempt to stay in your lane until level 6. By the time you are level 6 you should have enough gold to purchase sword of the occult.
Look around the map to see if anyone is medium or lower hit points, if they are you should use grand skyfall onto them followed by aegis of zeonia, spear shot, and heart seeker strike. You can swap around the spear shot and aegis of zeonia to fit your needs, ex: after aegis of zeonia if they are lower than 15% heath, immediately heart seeker strike them as it will critically strike them with every hit.
If no one is able to be ganked by grand skyfall just jump back into your lane and continue with the usual aegis of zeonia heart seeker strike combination harassment.
Continue looking around the map for chances to use grand skyfall to get your sword of the occult stacks up.
Remember, you are a very squishy cannon with this build so play accordingly, ex: Don't be the first one in team fights, if you play it right, you will be able to get to 20 stacks and almost one hit anyone with the stun, spear, heartseeker combo. You will also be the deciding factor in team fights in how you utilize your stun and aim your heartseeker strike to hit as many champions as possible.