INTRODUCTION

After playing many many rounds as Pantheon I finally discovered the (for me) best item build as him. In the end of games you can get up to 500AD with this build, if you keep the stacks of bloodthirster up and dont die.
In early game this build is also very good, when you get manamune you can kill enemy heros very easily by just using q w e q, if the enemy is not a tank, then he should die or you can last hit him with the passive of Heartseeker-Strike. When you are lvl6 you can start ganking, use your ulti to jump onto enemy heros stun and kill them in an instant.

Skill Sequence

First you take Spear Shot, so that you can use it to last hit the minions to gain gold.
On lvl2 you learn Aegis of Zeonia, when one of the enemys is on low health you can already start harrasing him, or kill him.
On lvl3 you take Heartseeker-Strike and start harrasing enemys, you use your Spear Shot, then you jump on them with Aegies of Zeonia, then you use Heartseeker-Strike to deal some serious dmg to them, afterwards you can use another Spear Shot if the enemy didnt flash / ghost away.
After that you need to max Heartseeker-Strike, because its the main dmg you do as Pantheon.
On lvl6 you take your Ulti, and start ganking other lines (ulti got nerfed, the range got rapidly decreased, so you cant jump from bot line to top line anymore).
After you have maxed your Heartseeker-Strike you start maxing your Spear Shot, because this attack also deals a lot of dmg later. In the end you max your Aegis of Zeonia.

ITEMS

Manamune: This is a good item for Pantheon, because it gives mana, mana regen. and converts mana into AD dmg. Mana is important for Pantheon because most of his dmg comes from his abilitys which are based on AD, and with Manamune you can spam your Spear Shot.

Boots of Swiftness: I take this item because as Pantheon you dont have any abilitys to escape. You run faster and when you use ghost, almost no one can catch up to your speed. Also its good for chasing enemys. You chase them then stun him, and the team has time to catch up and kill him.

Infinity Edge: This Item is good, because it gives you 250% crit instead of 200%, which is good for Pantheons passive ability from Heartseeker-Strike (100% crit chance against enemy with 15% health or less). Also it gives alot of AD which improves your dmg insanely.


Last Whisper: I take this item, because it gives you 40$ Armor Penetration, and is a good bonus for your Armor Penetration Runes. This lowers the armor of the enemys which increases your dmg on them.

Bloodthirster (2x): I take this item because of its AD, it gives you 60AD and lifesteal, also with each minion kill it increases its dmg and lifesteal by 1AD and 0,25% lifesteal. When you get 40kills, it grants you 100AD (x2 because of 2Bloodthirsters :))

You can also replace one of those Bloodthirster with Sword of the Occult when you got a good run and dont die too often.

Masteries

My Masteries are 21/0/9.
I choose this Masteries because it gives you everything a Pantheon needs, CD reduction, AD, critical strike damage increase, mana-, health regen. In my opinion these Masteries are perfect for Pantheon :).

Summoner Spells

I take Flash and Ghost as summoners spells, because Pantheon has no abilitys to escape, also they are good for chasing enemys, stunning them and killing them.

Runes

I took these runes, because it grants you armor pen. (which is a must have as Pantheon) life runes and quintessences and magic resistence.
Armor Penetration decreases the enemy armor for your attacks, which means that you do more dmg on the enemy than normally.
Life runes and Quintessence, I took these because Pantheon gets focused in teamfights (thats what I experienced so far...). It is also good for the beginning, you have more 126 extra health which is much in the beginning and can give you the first blood.
Magic resistence, Pantheon is easy to kill with AP abilitys, since they are not getting blocked by the passive ability of Pantheon.