I copy/pasted this from an older post I made, give it a read.
Pantheon, league's resident spartan and general spear & shield wielding bad ass, is in my opinion one of the more confusing champions to face against(especially in lower elo) and also to manage. We have all heard: "Pantheon falls off" which doesn't exactly mean what you probably think what it does.
I'm here to explain the in and out of Pantheon, and you will probably not understand this all at once, so take your time. There is a conclusion at the bottom if you want the quick and dirty.
Who is Pantheon?
Pantheon is a Toplaner(Occasionally jungler) champion who not only is very abusive in the early games, but generates a ton of pressure all around him just from his intimidating muscles. He throws spears, he blocks autos, He leap-stuns, he leaps across the damn map, and he gets free execute crits! Pantheon is kinda a jack of all trades, Map pressure, Lane bully, Stun, poke, semi tanky, good engage and zoning. He sounds pretty strong, but in fact he is a lot easier to deal with than you think!
How does he work?
To understand how to beat Pantheon, we must understand how he works and what combo's and styles he will use to murder you, although hopefully you learn and counter that.
Pantheon's passive is surprisingly strong early, it blocks auto attacks and can be proced multiple times in a fight. Every spell/AA grants him a stack, at 4 stacks he gets a shield, shield blocks AA. Leap-stun W automatically readies a shield. His Q, or "omg-stop-spamming-spears-on-me" is kinda his signature bully skill, point and click damage at a flat and semi low cost, it can crit with his E passive. W Is a good engaging tool, but he trades off a lot of defensive power(Think Irelia E) when he uses it to engage, when he probably has his passive up already, wasting an auto attack block. E gives him free crits attacking enemies below 15% health. You can actually see your health by pinging it and it gives you a percentage... Plan accordingly. His ult, the iconic man drop can be extremely powerful and devastating, but it takes time, like Nunu's ult. Fun fact: Pantheons ult can be used to dodge Karthus R, as it has a 2 second channel then 1.5 seconds of Fizz troll poll invincibility, Karthus R has a 3 second cast time.
What should I look out for in lane?
WATCH HIS MANA
Pantheon is a bully, no doubt, he spams Q's until he can all in and kill you. Q costs 45 Mana, W costs 55 mana, E costs 45+5 per lvl, R costs 100. His mana pool is 317.12 (+ 31) - 844 at lvl 18. I expect you to be in lane no longer than level 11, so his mana pool is ~630 at that point, but early it's really bad. His full combo early of QWE is 145 mana, If he doesn't have that much, then he probably can't kill you as long as you respect his E damage, which hurts a lot.
TRY AND FORCE HIM TO POKE EARLY
His Lvl 1 Q damage is PATHETIC, 65(+140% bonus AD, which is like, 20 damage) but the cost is the same, 45 Mana, making yourself look juicy and throw those lvl 1 spears is a win. they scale base by 40 dmg per lvl which is pretty significant because the mana cost does not scale. A good Pantheon will wait till lvl 3 and have Q(2) and W(1) before poking.
CARE FOR GANKS
This is kinda just general knowledge, but even more so for Pantheon because in his kit he has the ultimate skill that make junglers drool, his W. Point and click stun, 100% reliable CC, which by the way has the same range as his Q, so if he can poke, he can stun.
HIS PASSIVE MAKES TOWER DIVING EASY
If you are taking to much damage from poke, just back or consider investing in a corrupting(if you have not already). He can easily just run under tower and smash you and block 2-3 turret shots assuming he does not start with W for an engage. If you can pop it before tower get's blocked, thats better for you.
ALWAYS PING MIA
Pantheon's ult can easily net him a few kills. If he is not in lane, even if he backed, Ping the hell out of it. Usually takes about 10 seconds to travel mid from top and about 15 to get from base to botlane. Don't let him surprise your teammates. ALSO, If you are shoving his tower and he is MIA, there is also a good chance he is just going to jump on you, if he ults farther back, just walk past tower, don't try to run back.
So, how does he "fall off?"
Pantheons effectiveness falls off late game because his passive is less useful, his Ult takes a mind numbing 3.5 seconds, and his short range lane bully skills are hardly useful in stand offs. PLUS to do damage, he has to jump in, and he doesn't really pull off the bruiser like Kled all that well, meaning he is squishy and pretty easy to peel because he only has ONE gapcloser that is effective in team fight situations. His zoning however, is as good as ever. His ult is massive and threatening, making objectives a lot more dangerous to contest because he will just man drop the pit and really bring the pain. Often in the late game it's about making picks or quick engages murder the backline, siege, etc. Pantheon really doesn't do these all that well considering his ult has a massive wind up, his W for catches works, but is less effective in team situations. He will still hurt, so don't go fighting him 1v1 cause you assumed him weak.
Other miscellaneous tips
He lacks the power spike most other top laners do when they hit 6, However he has a good chance to just stun you and run away laughing, don't be reckless in trying to abuse your spike, Pantheon doesn't care half the time.
Starting Doran's shield is actually not bad considering it heals from his Q W and AA, Corrupting and cloth are both viable as well.
Forcing trades early with him and then backing/TP often puts him in a bad spot in which you can control the lane better if he doesn't follow suit. This is pretty common, but it's really effective.
His wave clear is kinda crappy, E costs a lot mana and he maxes it second, so someone with some solid wave clear can force CS off him.
Shields are the name of the game, His Q is every 4 seconds(to 3.2 when he gets BC) and blocking his damage is the best way to burn his mana and keep yourself healthy. Buying pots helps too, Corrupting is a worthy buy.
If your jungler is ganking, tell him to not gank from behind, Pantheon will just W him and run away laughing.
Don't take damage like a bitch, If you can hit back, do so. Half the game is just telling him he is not free to do as he pleases, however early AA don't really help due to his passive.
His passive blocks all associated CC with the AA, Naut, Darius W, Blitz E, etc...
Good match-ups
Darius, Olaf, Shen. All for different reasons if you cant figure that out.