Hi, this is my first guide so please don't be too harsh. I was looking at builds for Pantheon and I realized something. No one had good synergy, and if they did it was very little. Now this guide just shows you how to be a real jerk with Panth. You'll get very mean hate comments. At which point I would advise you to tell them "THIS IS SPARTA!!!", it just makes for a laughable moment. In which you'll have many.
My playstyle with Pantheon is very aggressive. Pantheons moves act on burst damage followed by a small cooldown. So to get the best results be aggressive, but not overly aggressive. At level one there is no need to turret dive, that's just stupid.

The runes are more of a tankish build. Which makes all the difference. Armor pen helps with your damage output. Health will help with survival, as will magic resist. The magic resist is because this build doesn't have much magic protection. Mages tend to be squishy so you should have no problems.

I'm going to start with the frozen mallet. You'll need health from all the aggro you'll be pulling, and it makes it harder for them to run away (which is always a plus). The boots help to take advantage of his passive. the faster his attacks the more attacks he blocks. It's very simple really. Youmoo's helps with cooldowns, crits, attack damage, and armor pen.
Infinity edge is a must!!! it increases your crit chance, crit damage, and attack damage. Throw in the heartseeker buff and BAM!!! This is where Warmog's armor comes into play. You will be killing things lots of things. You will go and things will drop dead. At max health bonus you'll be at over 4700 health, and you'll need it.
Atma's Impaler then becomes necessity. Two percent of your max health is converted to attack damage. Thats a bonus attack damage of just under 96 points (with health buff from warmogs). Now you get to watch the bodies hit the floor.

The summoner spells help early game for kills and they'll still have they're uses in late game. Exhaust also helps with your defense because it lowers their AD. Ignite does true damage so it's just awesome. You don't have any escapes with panth and his S.P.'s shouldn't be either.
I have ran a little bit then ambushed them for a kill.

You want all three basic skills asap. You get the heartseeker buff and you get a stun. which helps early through late game. First is spearshot though, you do need a decent ranged attack for when they run. Max it by level 9, Aegis by 13, and heartseeker is last ( I don't use it's active too much really). It's common sense to get your ult anytime it becomes available.

Your ult is extremely usefull. Great for jumping across the map. Awesome damage output. And HARD TO GET KILLS WITH IT, unless you use it strategically. Get them when they're busy. If they get busy fighting minions, BAM. If it looks like they're going to run from your team members, BAM. You'll get better at placing them the more you use Pantheon.

This build makes for an incredibly fun experience. Even if you are losing the match your kill death should be positive. You should work on your taunts with this build too. Dance at the bottom of they're nexus so that everyone sees it. Yell this is Sparta occasionally, and have fun. Before I forget, be aggressive.