Greetings, I am a jungle main that recently stumbled across the idea of using Glacial Augment on Pantheon jungle to secure early kills and help your lanes carry you late game, where you will most likely start to fall off.
Why Pantheon Jungle?
Pantheon has a point and click stun and a built in slow on his Q Comet Spear. His early game dueling prowess is strong, but he is even stronger at assisting teammates in fights. These combined make him a great choice for ganking aggressively early game. In addition, after he hits level 6, the range and speed of Grand Starfall will allow him to secure free kills on overextended or out-of-place enemies, and roam the map effectively.
Why Glacial Augment > Conqueror?
Pantheon jungle is extremely gank dependent. Suited to duels and skirmishes, Pantheon will inevitably fall off. So instead of strengthening his dueling with Conquerer, why not make his ganks stronger so that you can help your lanes get ahead, and win the game from there?

Summoner Spells
Smite + Ignite: The classic setup if you are looking to secure first blood and early kills. Remember that ignite reduces healing, so time your ignite depending on your gank target.
Smite + Flash: Less aggressive, but you get more utility with flash, and always have something to fall back on in case something goes wrong.
Smite + Teleport: In truth, I haven't tested this yet. But it seems to increase Pantheon's presence around the map, and with good coordination, you can get some kills while being everywhere around the map to help your teammates.

Runes
Glacial Augment - Pantheon's follow-up attacks on his empowered W procs Glacial Augment, slowing them after the 1 second stun is over. This gives Pantheon a window to get 2 more stacks of Mortal Will, empowering his Q, which deals a lot of damage and slows the enemy.
Magical Footwear - Perfect for Pantheon jungle, as you'll be racking up takedowns early, and get Tier 2 boots earlier, which will increase his roam potential drastically.
Biscuit Delivery - Honestly, this part of the inspiration tree is the most underwhelming. 10% Health and Mana restoration is great though.
Approach Velocity - Synergises with Glacial Augment. Also, if the enemy is too far to land a stun, you can throw an empowered spear at the fleeing enemy, slowing them and allowing you to reach them to land the stun. Both Cosmic Insight and Time Warp Tonic are decent choices as alternatives.

Cheap Shot - You'll be attacking slowed enemies a lot, so this outvalues the burst of lethality you get from Sudden Impact.
Relentless Hunter - More roam.

Press the Attack - This works well against tankier laners, and as a bonus, you stack it instantly with your W. It will help you isolate targets for your teammates to kill as well.
Conqueror - Normal Pantheon rune. You get healing and AD, but less aggressive ganks.
Electrocute - Works well against squisher laners.
Hail of Blades - Wut? Why? it might help stack Mortal Will if you don't like your empowered W, but other than that...

Items
Duskblade of Draktharr/ Youmuu's Ghostblade/ Edge of Night - Gives you a ton of burst. Scales well with your Q and E, so you'll be building these after your jungle item most of the time.
Black Cleaver - You get 3 stacks instantly, shredding armor. Gives you health and CDR, so overall a great item.
Mobility Boots - I love these. You can be everywhere at once, setting up ganks easily, saving time to clear your jungle, etc. You can change the boots depending on the situation, but I LOVE mobies.

Skill Order
Q > E > W To start if you want to clear the raptors after doing red. A really efficient clear, but you sacrifice Lv2 ganks.
Q > W > E If you're looking to immediately gank after hitting 2, or maybe clear Krugs/Gromp and gank.
Max Order: Q > E > W
Q is the main damage dealer of your kit, max it accordingly.
E deals a decent amount of damage, and helps your clear your jungle more easily.
W can be maxed last, but if you want shorter cooldowns, feel free to max W before E.

W* > AAA > A > A > Q*
This is the reason for running Glacial Augment. You get a window to auto them twice to fully stack Mortal Will, and follow up with a tapped Q for damage and slow, or finish them off with a charged one, and save E for potential tower dives.
W* > AAA > A > EE > Q* (Auto Reset)
The largest amount of damage in a short period of time. After this, you'll have no abilities remaining, so be wary. Remember that you can hold your Q to deal increased damage if they're below 20% HP, so you can finish them off if they flash away.
W* > AAA > EE > A > Q*
Same combo, but you hit your E first, dealing more damage toward the beginning. Only issue with this combo is that if they flash away after your E, you can't auto anything to get the last stack of Mortal Will.
Q* (Held) > W
You slow the enemy with your empowered, held Q, proccing your Approach Velocity and letting yourself into W range. Kind of weak damage output - you can use this to let your laner catch up with your enemy.