Not Updated For Current Season
First i'll explain my pregame set up.
Ghost: absolutely amazing for panth from what i've seen. great for those oh **** moments as you see mid jumping into your lane after you just took out both of your lanes heroes. Also great for getting that last spear shot on someone
Exhaust: fantastic first blood tool. Great for shutting down someone like jax or yi if you get a bad start. Add in the extra Arpen you get from throwing it on someone and it just shines that much more
Ignite: great for tagging that pesky tank (shen) that's good at escaping with an infuriating 20 health. I've found its less useful tho as I go for nuke panth and not many ppl survive throw me jumping on them regardless if I have ignite or not.
Flash: another great choice for escaping or initiating from a fair distance away to catch the enemy off their guard. I like ghost over it tho, just because it can cover more ground. Still some ppl cater their play towards and really like it.
Panth is a melee carry. Sure you can build him tank if you really want to but the amazing dps potential you can get from him far outweighs a full defensive build imho.
Arpen, arpen, and more arpen. Everything panth does is physical with the exception of his ult. Next the dodge is for synergy with nimbleness and it gives you a lil more survivability. Finish up with CDR as panth is extremely cd reliant.
Spear shot: A great harass. Very effective really early game when you roll up and punch a quarter of a squishy's health with a very short cooldown. I also use it as a finisher if my heartseeker didn't just take them down by itself. Also great for nabbing runners as they try to escape with a sliver of health.
Aegis of zeonia: This is your initiating button. Get you there, keep em there for your heartseeker. Great set up button. With the change for the increase of stun duration i like lvl'ing this up second in case i'm slow with slapping down the heartseeker cuz i wanted that perfect position to get as many ppl as possible with it.
Heartseeker strike: This is what makes you a monster. Your bread and butter. Jump on someone with your stun and watch their health melt away with this. While its a great farming tool as well due to the aoe cone, if there's enemy heroes about I strongly recommend to hang on to your cooldown in preparation for a gank as you should be harassing with your spearshot.
Grand skyfall: A world teleport similar to TF's cept this one does damage. aoe damage to everyone in your circle. While very unlikely you'll catch anyone in the center, it is pretty reliable to catch them in range of your aegis so you can immediately jump and finish them with a heartseeker. Great if you can make them hesitate by pinning them against a turret.
The item build
Health and mana pots with boots of speed: I like having health pots so you can get away with some agressive behavior early and not have to go home every lvl. Boots early makes it easier to get in and out for those spear chucks or to rush someone. Also he is very mana hungry through out the game so either pick up mana pots or grab a golem buff to sustain your thirst.
SotO: Obviously if you're new to panth, taking sword of the occult might not be a great idea. I would suggest just skipping it and getting an additional bloodthirster.
Brutalizer: Arpen is great for panth. And cooldown reduction makes it so you can jump/hearseeker someone that much faster. Plus some AD? Yes please!!
Infinities edge: You know how you got that cool buff saying 15% or below is an auto crit? why have to hit them twice? with this you even make blitzcrank's mana shield go down with one shot.
Bloodthirster: A little life steal never hurt anyone. And there's always that point that as long as you can keep the bonus rolling on bloodthirster its the strongest AD item in the game. So yeah, nuff said.
The cleaver: Yeah AD!! and arpen!! but there's always those points in time where you really dont need anymore arpen for their team. Sometimes they're not too bright and won't stack armor against you. Then leave this for another bloodthirster instead. lifesteal is better than wasted arpen.
Yoyo blade: Remember that brutalizer? Time to upgrade as we have the more important items now. Plus ghostblade makes you run faster to chase someone down or to go toe to toe with the tank so you can get that shield procced even faster. Its great for turret diving too as that shield will eat a turret shot.
The important part. You can hand someone a rocket launcher but it doesn't necessarily mean they know how to use it correctly. I'll try to break it down as the game progresses as to what I do.
Early game: Spear shot, again and again and again. When you get to lvl 3 this is where you move in for the kill, unless of course they're completely ******ed and allow an easy kill earlier. You kinda want to play defensively without your cooldowns up and even with them up, this early you don't do massive amounts of damage due to scaling off AD so much. So wait it out. Go slow and immediately go home when possible when you got the cash for your boots and SotO. When you get a few stacks up and brutalizer rolling, things really tend to die quite fast.
Mid game: Its prime time to go hero huntin'. You even got a nice ult to get back to your lane when they get kinda close to your turret. Its fairly easy to just go wait on mid's bush. More often than not mid is some incredible squishy and is prolly around half health just from being in mid battling it out. A quick jump and heartseeker is a pretty much guarantee for a quick kill. Also be on the look out for them bunching up for team fights. You get 3 or so in mid with all 5 of them pressing down on your turret you can turn around that depressing situation as dropping in scatters them. You usually kill one, 2 if someone is nice and has a disable right next to the guy you just jumped. Be on the lookout for grabbing more than one with your heartseeker.
Late game: If you aren't the main focus of team fights by now consider yourself lucky. You should have enough AD by now that your spear is taking away half of ryze's health away and if you get a jump on him its a lol situation. This is also where I tend to get a bit reckless and get away with it. Skyfalling ontop of them while they're turret hugging and killing 3 of them before ghosting out is just ridiculous. And when it starts to happen you tend to either get a surrender or alot of complaining lol.
One thing I would like to make sure I get across, this makes for a squishy panth. Don't be lulled into a sense of security by being all that in your lane and then have your *** handed to you as you try to take 3 of them on at the same time. If you stay alive those stacks will come with time and so will the destruction of the heroes you pit yourself against. Also sadly if you start out slow, the entire game appears to slow down for him, as it is for alot of carries.
Heroes that have a snare/stun/slow are group to group up with in a lane as well. The best hero ever to lane with you tho is soraka. If she's there push hard for her to follow you around, you'll never have mana issues and you can likely get away with being completely reckless. It makes for good fun and an absolutely ridiculous score. My best run came from a soraka in my pocket and went 40/2/12. So good luck out there and may your spear find its score :)