This is my very own selfmade Pantheon guide. As you can see im going with 21/0/9 to get the extra damage in the Offense tree and the increased XP in the Utility tree, I've just recently bought Pantheon myself and i recommend him strongly, hes a nice initiator with his ulti, hes stun is very useful if u want to jungle with him. (I will make a jungling guide for Pantheon very soon)

For runes i go with full Physical attack runes, following..

9x Greater Mark of Desolation
9x Greater Seal of Strength
9x Greater Glyph of Strength
3x Greater Quintessence of Desolation

Why?

It's very usefull in early game to harass ur enemies, and other runes aren't really needed (MR/armor runes) because often you will have a tank in your team who will take aggro and you'll be free to just spear them all down

For masteries i go with 21/0/9

why?

Im going this way because i want and "need" the extra damage from the Offense tree and also i get some CDR on the way and also the extra armor penetration ofc.
The rest i drop in the Utility tree to get improved ghost and the extra XP and increased time on buffs, since i don't play with mana regen runes it can be needed in necessary situations

For items i start of with a Doran's Blade, then i go back and buy boots of speed and another doran's blade when i feel for it and when the enemy team isn't pushing, i continue with a BF sword and if u got some left overs, buy a Long Sword, the Long Sword goes either to The Brutalizer or Sword of the Occult, depending on if ur confident on your team and if you know u can stack it up. Else you will go with The Brutalizer to get some armor pen/AD, then continue with getting your second grade of boots (Mercury Treads) and a Bloodthirster, after that i buy Pickaxe and takes that into a Last Whisper. After that when you got the money i buy another BF Sword to get anothe Bloodthirster to get some more lifesteal, and i finish off with a Frozen Mallet.

Im trying to get the Spear Shot and Aegis of Zeronia maxed first to make as much damage instantly to my enemies, So first i go with Spear Shot to harass my enemies early, then i put a point in Heartseeker Strike to be sure that i will get my crit to kill the ones who think that they can run away from me. then i go with my Aegis of Zeronia and starts to harass a little more. Just be CAREFULL with your mana because we don't play with mana reg runes here! :P. Putting points in ulti at 6/11/16.

For summoner spells i go with Exhaust andGhost,

Why them?

Exhaust is good for preventing enemies for fleing or making loads of damage to you/your team mates.
Ghost is a nice catch up/escape tool, flash is an option aswell but i prefer ghost

the Pros with Pantheon is that he can makes loads of damage already in early games, he can help out very fast gank good with his ulti. Hes also an amazing ganker for jungling with his Aegis of Zeronia.

the Cons with Pantheon might be that hes kinda squishy, can't really think of any more cons for him tbh, hes awesome

when you have around 200 damage you will be able to take out minions with Heartseeker Strike in just one spray, but in early games just wait for last hitting