Hello this is my first build starting Pantheon. Since most of the players aren't playing him a lot due to the nerf problem. I have developed a build which will not always win but to have fun. Your main objective when it comes to fight you have to either kill the squishies or damage dealer first. Capturing a single enemy champion is fine.

Pros:
Great Damage Dealer
Quick Eliminator
Surprise Attacks

Cons:
Wipes Portion of Mana fast
Fragile in early game
Can be stopped (Unless has Tenacity)

Greater Mark of Desolation Armor Penetration is important for Pantheon's Spear shot and Heartseeker Strike to be effective in battle.

I chose Dodge Seals because it's really useful during the fight. It'll grant you getting 1-2 dodges in few clashes.

There are reasons to pick magic resist for a melee person to be toughen up while leveling.

Greater Quintessence of Desolation PENETRATE through armor sinking their life.

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Cripple: Best improvements for Exhaust.
Sorcery: Will grand useful cooldown reductions.
Archaic Knowledge: Will grant magic PENETRATION.
Brute Force: Will increase both of your physical damage abilities.
Lethality: Is very effective against high HP champs and last hitting
Havoc: Stop hatin'

I buy the Long Sword first with Health Potion because it gives additional damage for your Spear shot and Heartseeker Strike and it's important to get The Brutalizer ASAP.

Mercury's Treads is one of the useful items for Pantheon to return to his work after being disabled.

The Last Whisper is my favorite weapon to purchase for Pantheon. It goes well with Brutalizer giving your enemy a blow damage.

The Phage would balance your taste around the battle giving you a survivability as well a chance to easily kill an enemy.

Superior item for Panth to increase his damage output and staying on foot.

Buffing him temporarily to get use for his lifesteal and attack rate to regain his strength.

Upgrade of Phage enourmously increase his health use for his Bloodthirster with the slow applied on-hit effects.

Spear shot is used to get champs inrange or last hit minions dealing big hurt to them.

Effective to hold your opponent's down while you or your teammates are casting abilities.

Best offensive skill to quickly devastate your enemy and be wise where to place your spear.

Make sure you time and place your landing spot where your enemies movement comes at giving you successful combo. It is friendly if your teammate knows when to immobolize (if you have any of them) right at the 33% center radius damage.

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Many reasons to use and save it for later. Benefits to debuff tough enemies or quickly kill an enemy who is likely to escape.

A great surprise spell to catch up to an opponent either you throw your spear in the back or bash em' close with your shield. Also for escaping tool.

Heres a fun trick to pull off on your opponent. When laning, if you got your opponent's health about 50% below average and he/she still pushes. Go hang around behind your ranged minions. Before deploying check your Flash and Aegis of Zeonia radius. If you think you can make it go ahead stun him/her then use Exhaust (optional) quickly and then swift strike. If that thing is still alive then just spear him/her untill she dies. *Note: Don't overextend that much, if your certain to comeout alive from their turret.

If someone is chasing you with full health and your about 1.5/4 HP that you know you killed him/her before a lot or easily. Then man up and fight with your Heartseeker Strike and such whatever you have left upon to cast. REAL MEN FIGHTS TO DEATH!!

If your doing fine it's best to keep your playstyle you did in early game instead of you thinking you can do something to kill most champs. Late game will get intense a bit but with your teammates help including your PENETRATION, you will be victorious.

Q. Why didn't you get Doran's Blade instead of Long Sword?

A. I know Doran's Blade gives additional health and lifesteal including damage but getting the Brutalizer will take you extra 415 more golds in process

More question awaits...