Ok, obviously AP Pantheon isn't supposed to be done in a serious game, unless you're THAT good.

Even then, LoL is about fun, so yeah, Dar-

Pantheon is fun.

Pros:

-Great Burst, and AoE damage from Grand Skyfall and Aegis of Zeonia
-Can't be countered by Banshee, as he can get rid of it with either his AoE "unshielder" Heartseeker Strike, or his more accurate Spear Shot
- Still has decent Physical Damage, as his attacks have the critical chance from his Heartseeker Strike Passive
- You will be building CDR, so you get a stun every 5.4 seconds, letting you be more useful utility wise
- You have two abilities (Spear Shot and Aegis) to activate Furor, and with Rylai, you can kite
- You will have your passive up more, as you can not only still use his regular physical abilities, but you can get it through your max cdr Aegis

Cons:

- No sustained damage
- After combo, you're very vulnerable, especially to people with high damaging abilites
- Anyone with a dash can avoid almost half of your optomized burst
- Magic Resistance can counter you very well
- Can be hard to land Grand Skyfall

Get dese two, because you're here to kill things, not to flash away, then W.

You could barrier to survive until you get your W again, but it's very situational.

Some tips and tricks, mostly revolving around his passive, Aegis Protection

Early Passive Gain
#1 - At base, you can stack his passive if you have his E. This is really only useful if you take and early E because you'll be in a teamfight, or you're in Dominion, with at least one point in your E

Double Passive Stacking
#2 - Every time you attack you gain one stack of Aegis Protection. At four stacks, you get the Aegis Protection buff. If you use Aegis of Zeonia, you gain the full Aegis Protection buff. This means if you manage it right, you can gain three stacks with your poke Q, and jump in, with the Buff and 3 stacks, meaning right after they attack you, and Q, or AA them to gain the buff again.

Quick Passive Gaining
#3 - Your Heartseeker Strike gains your passive really quick, and you can do a triple attack at close range with AA,Q,AA. You can gain 3 stacks of your passive almost instantaneously, and this can save you, or help you in trades, etc. Because you're AP, you should be using this to help you survive, and if you can, let your teammates kill them, or let yourself get your W cooldown to kill them again.

Getting Rid of Pesky Spell Shields
#4 - You have your Q and E. Even though your Q and E don't do that much damage, you will still use the Q to finish people off, and your E for passive. Even if not, you can still break spell shields with them, and use his Q for your Furor passive, if you get it. (Shoe enchantment)

Grand Skyfall stun???
#5When you place your ult, you can use your ability while Pantheon lands. Do this by placing your ult, and hover your camera over the landing area. When Pantheon finishes jumping, you can spam your skills to land them. You usually use your W during your Ult for normal bursts, but if they are not budging, you can Q them first, then W, E, AA, Q, AA them.

Hope these tips can help you out, for AP Pantheon, and maybe even AD Pantheon!