NOTICE: I no longer play Pantheon, and I never updated this guide after he got nerfed. I have no interest in doing so either, and as such he is archived. You can use this if you want, but it's far from up to date.
~ Dalek Jace

Everyone knows Pantheon, but few know him very well. His look is great and pretty tough, he looks real strong and therefore is a quick buy for new players. Personally I've seen the number of Pantheons I play with or against decrease over time, I got the idea this is because at low level people try the champions out, while at late game they know which are good and pick from those.
Because Pantheon is played by poorly skilled players a lot, the thought people get is "food". This is usually true, unless played right. Pantheon isn't just a burst within his cycle, but can actually take on two or even three players on his own, while at the same level. This, while he has no significant AOE spells apart from the recently buffed Heartseeker Strike. His passive - Aegis Protection makes him an excellent towerdiver, if necessary at all since his Spear Shot has a huge range.
The placement of his ultimate can make or break a teamfight, gank or quick push.
Your team has to know what to do, they have to know what you can and what you can't. You have to be prepared to sacrifice yourself to give your team the winning edge. Getting 10 kills early in the game doesn't mean you'll carry your team, as you'll be taken down rather quickly without any escape possibility (except for summoner spells).
You take carries down in one cycle and one or two seconds, or get your *** out of there. You take down that support, and you spike that runner into the ground with your spear, but you won't stand ground against a good team on your own. You are not an end-game carry.
Keep this in mind while you play, because taking down that Gangplank and then getting shot in the back by Miss Fortune isn't going to give your team the victory. You take that Gangplank and get your *** out of there. You don't risk your life, you take what you can get and not more.

(Innate) - This spell can make or break your kill. Keep in mind that this is also refreshed by Aegis of Zeonia.
It's fairly simple to comprehend, but is often forgotten to be "used". When you start a tower dive, you can throw your spear and run in. Block that first tower hit, then use Aegis of Zeonia to stun (and refresh the shield). Block another tower hit (probably the second). Use your Heartseeker strike and possibly one last stab, and get your *** out. You'll get away with a kill and barely a scratch. If you stun before the first tower hit, you will block a hit less. Remember this, always.

This is your main spell. Heartseeker Strike does more damage, but the cooldown on this can go down as far as 2.4 seconds (4 seconds normally) Mid-game this ability can hit for 500+ damage, and that on a few seconds cooldown and long range. Throw this as much as you can. One shot that minion, throw it at the champion that comes too close. It doesn't matter. After your Manamune or Chalice, you won't run out of mana anyway.

Best known for the combination with Heartseeker Strike. That 1.5 second give you the time to push them to <50% health with only these two spells.
It has more uses though. If at rank 3 or higher, the stun is long enough for you to get your run if you have to. And as said at Aegis Protection (above): It refreshes the shield you have. Excellent skill to towerdive and get that towerhugger.
A good way of getting away from someone that's trying to finish you off, is to hide on the edge of some brush. When the attacking player is about to enter the brush, you stun him/her and run like hell. Make sure you use this only when it's smart, but it can safe your life.

Since this got buffed it's incredible. Aegis of Zeonia is getting a nerf and will only be a 1.5 second stun, meaning the player can move out of Heartseeker Strike if they're paying attention. This means you'll have to position it a bit different then before. try to aim it in such a way that he either has to move through it or move in the wrong direction (to your team, your turret, whatever). Although I must say that I don't think anyone will be able to move out of it, as it's a cone.

A skill that's hard to master, but incredibly strong if in the right hands. Especially great in the teamfights. When everyone is in chaos, or when that Amumu uses his annoying ult you jump in. Nobody is going to spot it in time to completely dodge it and they'll get a minimum of about 350 damage each.
Something a lot of people don't know, is that you can cast your next skill while dropping from the sky. It'll immediately throw that Spear Shot or Aegis of Zeonia as soon as he lands. You can hit that runner in the forest, you can push that tower and even inhibitor while the rest is on the other side of the map. It's got a lot of uses, you could even consider to farm a big batch of minions with it if you want. Don't be afraid to "waste" it. It's not your core skill, so don't save it for when you "need" it.

Tip: Grand Skyfall can be repositioned by the use of flash after the circle has been "drawn" on the battlefield. This means that you can still land on someone's face, even if they tried to move out of the circle. (Haven't tested it myself, someone told me. Cred. to him)

Note: Items shown in the cheat sheet are what I try to aim for. By all means adapt. It's a guide, not a manual.

Core

You need that mana and that regeneration. You'll end up with around roughly 2200 mana and an extra 60-70 Attack Damage. You can switch this for Chalice of Harmony, but you don't use that much mana, you just need more then what you normally have. The 7 mp5 is enough regeneration, and the extra AD helps a lot. It is a more expensive choice though.

This is my main choice of boots, due to the attack speed to refresh that shield and get those extra hard hits in. If they got a lot of CC, you switch to Mercury's Treads. I barely ever get Ninja Tabi, but it may also be useful. Keep in mind that if you switch those boots, you will miss the attack speed.

Shouldn't need that much clarification, but some things should be noted: Heartseeker Strike's passive gives you 100% crit chance at targets below 15% health. With the Inifinity Edge and the Crit Damage runes you'll hit that last health off in one or two hits, as you'll hit for roughly 275% of your normal damage.

Pretty straightforward, nice attack damage and the 40% Armor Penetration rips that Rammus to shreds. Trust me, he won't dare to taunt you again.

Optional

Also pretty straightforward. You can even stack two or three of these if you want, but one should be more then enough. You shouldn't be in combat for longer then a few seconds and a one or two kills. The attack speed will make you trigger Aegis Protection often in your fight and can save your life. (If you do good in the start, you'll be a - or the - main target, and you'll need that shield) This will also total your crit chance at 52% (50% without masteries) which is nice with 275% Crit Damage.
If I use the Berserker's Greaves I always end up buying an extra one of these and selling those boots. You won't lose movement speed and have much, much more benefit of these blades.

As much as the Last Whisper shreds that armor already, this will leave nothing to cleave through at that tank. Since it also adds Attack Speed now (and a bit less damage) it's a very good item. However, it's still a waste of money if you don't play against something that needs this extra armor reduction. You could swap Last Whisper for this though. Depends on the amount of money you gain. It needs to build, and if that carry stays in range of you for long enough that you can build those debuffs, they're either dead or you're doing a bad job at it. So use this if you really need it, if you just want the extra damage try something else.

A great option of you're dropping health quicker then you like. You burst so much damage out that you may get out of that fight with more then 90% HP left. It's always a hard choice, but you probably don't even get to buy this item.

I always recommend that a teammate builds this. A Sivir or something would make more use of this. Nevertheless, if you prefer the extra attack speed or want this in combination with the Black Cleaver (And instead of the Phantom Dancer) you could go for it. I don't like it in my inventory, if I need the lifestealing I prefer the Bloodthirster and Phantom Dancer.

I never get this, I don't need it. But it's an option, for sure. If you get a lot of runners or need that extra pack of health, it can save your life. (Spear Shot while you run = slowed chaser or runner). However, I never get to the point where I would need this. I don't even consider it, as I'll just get Bloodthirster instead of the health. The shield should do the rest. But it's within your grasp.

Games usually end before I get to it, but it's a great item for you nevertheless. If you get into a battle on your own against two or more enemies, you should be able to either take them all down on your own, or buy enough time to get regrouped with your teammates. The time for it to trigger is about 4-5 seconds if I'm correct, which should be more then enough to get that tank close to you. Otherwise, just take two or three people with you into your death. It's usually worth it.

Not-to-take

I've seen numerous Pantheon's get this. It is only good if you get enough health for it to count. With 2000HP at level 18, this won't give you more then 40AD, which is nothing compared to a Black Cleaver or Bloodthirster.

This is only useful if you get it filled, which will give you 110AD and 15% Movement speed. It's nice, it's cute, it's not good for you. Pantheon is squishy as hell. You die when the enemy team wants you to die, unless you're lucky. If you start stacking this they are sure to attack you. If you can't let it go, go for it. If you can keep the stacks it's nice, but I would prefer the other options, just like Atma's above.

Masteries are always a bit of a hassle with Pantheon. Some want to go fully offensive (me), and some want to scrub his squishiness away a bit. Either goes, both have potential. This is my style, but by all means check out Chaotic Bliss' - Phalanx of One guide. He's going more defensive, which might suit you more.

Anyway, onto my choice of masteries: 22/0/8
I think my offensive choices are pretty obvious.
Sorcery is very good for the spears you got, you want to throw those as much as possible. It may just get you that one Heimerdinger that's running away!
The Utility is just my personal choice, if you want the rest in Defensive, go ahead. It's a personal taste, so make it your own choice.

First of all, I'm not a pro when it comes to runes. This is what I chose, but choose what you find best.
I use Greater Mark of Attack Speed to get my attack speed very high at the start already, but you may switch these for Armor Penetration or Crit Chance/Damage runes if you please.

The rest goes into Crit Damage completely, including my quints. If I get someone below 15% health, he's dead. No way he's getting out of it. I'll rip his head straight off, because of the 100% crit chance you get from Heartseeker Strike.

However, if you are going defensive with your masteries, you might want to do this with the runes as well. I'd go offensive with the marks, as that's where they're made for anyway. But you can go for Armor, Magic resist and hp5 seals and glyphs and for flat health or health/level quints if you prefer.

Also these are a matter of - you guessed it - personal taste.
Cleanse is chosen because I don't usually get Mercury's Treads, I like it to save my *** for me if I find that Sion's Cryptic Gaze to crash into my face again. It saved my life hundreds of times, but you need to get used to it. (A lot of people forget about it, use it too late, or use it when they're better off saving it for later)

Exhaust is useful for that runner, but also for that Yi that you are dueling. A good Yi may win the fight normally, but by combining stun > exhaust (blind) > stun, you will most likely punch him into the ground.

Other good choices would be:
Flash is always good. You can chase with it, or get away with it ( Ghost is better for chasing, in my opinion). It's also good with Grand Skyfall (Read the tip in the Spell Section for that)

Ghost is a great chaser or runner. It's better then Exhaust to chase with sometimes, but Exhaust is far better if you're playing with your team. And again, Exhaust can help you in a duel.

Ignite: I don't like this on Pantheon at all, but maybe you do. The only reason I'd use it, would be for the 50% less healing. Good on Warwick or someone that stacked Lifestealing, or that Mundo with his ult on.

Note: Changelog contains major changes and things users should know about. Typo's and such won't be shown in here, it's not subversion >_>

18th of November, 2010

• Initial build. Not yet complete, more information will come during the following days. It takes some time to write this in a sense that people can understand...

24th of November, 2010

• Added a tip about flash with Grand Skyfall.
• Added Masteries section.
• Added runes section.
• Added Summoner Spells section.

18th of January, 2011

• Used the new system of Mobafire on chapters etc. Great job from the Mobafire staff, this is so much better!
• Updated it since things like Aegis Protection and Heartseeker Strike had some intense changes and.
• Went over every section and rewrote some things, fixed some grammar and added some extra things, it's just better now :)
• Updated the Summoner Spells section to look better. It was a mess.
• Updated the Skill Sequence (Cheat Sheet) to represent that Heartseeker Strike is buffed.