Jayce is a hybrid champion, combination of melee fighter and marksman, champions like this are really hard to play well but they also can be the most overpowered source of damage in your team. Here you will learn how to use jayce hybrid potential in jungle.

It's probably obvious what items you should start on jungle, so I won't talk much about that, its absolutely essential to finish Spirit Stone real quick, you need to have it after first recall.

I use most basic ad runes that works great on jayce in the jungle, but you can try typical jungle runes with mark of attack speed on quint of movement speed, it also works

When i Started to play with jungle Jayce sustain was my worst nightmare so i was playing with 9/21 masteries, for now i found out that 21/9 are the best masteries to use Jayce well.

Starting with maxing your w helps you during the jungling, but Lightning Field is not scalling so good and it wont give you good dmg so i start with maxing Q ( Shock Blast, To The Skies!) that gives you a lot more dmg during ganks, then you go E, for better scalling of Acceleration Gate and Shock Blast combo and %hp dmg from Thundering Blow.
So this is how it should look like:
And this is optional that is not so valuable, but can help you aplyred buff effects or Blade of the Ruined King if you decide to rush it early

Generally forget about Tear of the Goddess while playing Jayce on jungle. First Jayce have no mana problems at all. If you have Spirit of the Elder Lizard or even Spirit Stone its hard to loose mana while jungling. Then if you buy Sheen its nearly impossible to loose all of mana jungling and ganking. I know that Essence Reaverseems to be made just for jayce, but there is no need to buy it when you are jungling. If you really really think that you wont be able to fight because of mana problems, you can buy Essence Reaver intead of Bloodthirster or Blade of the Ruined King. You should totally forget about buying Manamune, it will be useless, trust me, it will! ;)

Most of jayce damage comes from spellblade passive, so you will need to choose between Trinity Force and Iceborn Gauntlet. You need to have something that gives you also attack damage, so we need to have a closer look at it.

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Blade of the Ruined King
I really like this item, it gives you awesome %hp damage, good attack speed that helps you with clearing jungle and great active while ganking, that lets you use passive Hextech Capacitor to avoid unit collision while passing throught slowed enemie and push him back with Thundering Blow. Blade of the Ruined King scales good with Hyper Charge

Bloodthirster
This items gives you good dmg, survi with passive and life steal, it's a good choice in a full damage build, but it's not enought valuable to repalace BOTRK.

Essence Reaver
If you have serious mana problems that even jungle item and Trinity Force cant help you with, that's item for you, simply the same as Bloodthirster, but hold your mana bar high.

Infinity Edge
DAMAGE! DAMAGE! DAMAGE! Critical chance is always good.

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I found BOTRK as essential item on Jayce in jungle, then you can choose one of those in
lategame.

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Now we will need some armor penetration for good dmg to an enemies, here we got 2 items to choose:

Last Whisper gives you good damage based on armor penetration, but if you are building tanky, it won't be valuable.

Black Cleaver gives you cooldown reduction, armor penetration, some survi and good damage, also great scalling with Hyper Charge so it's obviosly essential item on Jayce

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Now we need to survive enought much time to deal damage so here comes items that can provide us that:
Frozen Mallet
Jayce already have a mallet, why don't make it twice? This item gives you awesome survi and passive slow that is really usefull while ganking.
Guardian Angel
Everyone knows why it's awesome so just buy it! :D
Randuin's Omen
Great item versus heavy ad enemies, also makes your ganks better with active slow.
Banshee's Veil
Good vs heavy ap enemies, i'm sure it will piss off any support and apc.

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Here you got most items you can choose from, now it's all up to you.

So coming to items jayce is really flexible if it comes to items. When you're playing jungle it is essential to have jungle item, I usually choose between Spirit of the Elder Lizard and Spirit of the Ancient Golem. I played with Wriggle's Lantern, but i don't like it. It's up to you how do you want to play Jayce, we will now check what build is most valuable with what jungle item.

So for now, if you choose as you jungle item Spirit of the Ancient Golem It's quite obvious that you should go tanky, so good items choice would be Iceborn Gauntlet, Frozen Mallet, Guardian Angel and Randuin's Omen or Banshee's Veil(depends on what type of champions dominates in enemies team). This option gives you awesome survi with good dmg from scaling skills and spellblade passive. You shouldn't swap your Spirit of the Ancient Golem when you're building this way, better buy Elixir of Fortitude. If you choose to buy Spirit of the Elder Lizard You can go full damage choosing of all dmg items in game, i like to play full dmg with Blade of the Ruined King, Trinity Force, Bloodthirster and Last Whisper.
You can also build Bruiser Jayce with Blade of the Ruined King, Trinity Force, Frozen Mallet and Guardian Angel. This build i believe gives Jayce best ballance between damage and survi.
If you start with Wriggle's Lantern, you should build Essence Reaver as soon as possible. then you can combine every item i told you about just to make this game comfortable for you :)

On Jayce jungle Smite is essential, but on second skill you can take simply everything you like to play, i prefere Flash as escape option or to secure a kill using Flash and Thundering Blow to push enemy out of the turret range or right in front of my teammate, that i'm sure will take care of him. You can also use Ignite or Exhaust instead of Flash. I think Ghost is not a valuable pick, cause if you need movement speed you can take 3x quint of movement speed and Transformation and Acceleration Gate combo will provide you as much movement speed as you need.

It's pretty easy, you need to use Transformation as much as it's possible to be able to deal dmg with all of your skills and passive dmg boost. You need to use Thundering Blow wisely or even avoid it cause sometime you can pull monster throught the wall and it will only make you waste hp and mana. You can use Stealth Ward to jump over the wals with To The Skies! to clear jungle spots quicker or to escape enemies. You wont have mana problems on Jayce but it is still good to take blue buffs until you get yourself Trinity Force and jungle item.

Ganks are pretty easy, you start with your Acceleration Gate and Shock Blast combo, then using movement speed boost from Acceleration Gate and Transformation you need to get as cloose to enemy to use To The Skies! and while he is slowed cause of this you deal him damage with Lightning Field and try to pull him back to your allied champion using Thundering Blow, then you can finish him using cannon again. Pretty easy.

Jayce have good synergy with hard cc champions like Pantheon which can let him aim Acceleration Gate and Shock Blast combo easly and gives enought time to join the fight. Jayce plays jungle best with Xerath, Brand, Lulu, Leona, Blitzcrank, Pantheon, Shen.