Jungle Yi is a very fun jungle who specializes in farming up the jungle, getting fed, and dominating end-game. Moves such as his alpha strike assist him in screwing over the enemy jungler and his high attack damage helps him spring out of the jungle and demolish towers, fading from sight and inflicting fear in the hearts of the enemy team.

Keeper of the ancient art of Wuju, Master Yi is a mystical warrior from the isle of Ionia. He descended from one of the few tribes dedicated to the preservation of Wuju, a martial art founded with the principles of absolute spiritual awareness of one's self and one's enemy. When the armies of Noxus invaded Ionia, Master Yi joined in the Ionian defense to fight the craven enemy, bringing his village honor through his unparalleled mastery of the blade. The ensuing battles ravaged the land, but no conflict inflicted as much horror as the day the armies of Noxus closed in on Yi's village. Left undefended, the village became the unfortunate test subject of the latest invention by an up-and-coming chemist, now known as Singed. The remains of the village that Master Yi returned to were so horrific that it remains a festering scar on Ionian history. To this day, no Ionian will ever publicly speak of what occurred.

After the Noxian invasion was contained, Master Yi fell into a deep isolation. For years, he trained morning to night, speaking to no one and refusing offers of consolation by fellow Ionians. The only thing stopping him from madly charging into Noxus battle lines headfirst was his pledge to keep the Wuju style alive. Even though he seethed with impatience, his rage became a tool for sharpening his practice of Wuju, developing stronger and deadlier skills for his eventual vengeance. The only thing that roused him was news of the League's formation, and Noxus' subsequent enrollment in the League. Master Yi now brings his mastery of the blade to the League of Legends with unflinching purpose: to avenge his kinfolk and end the predations of the Noxus once and for all.

Pros :

Very good end-game
Reliable carry if your AD carry messes up
Can build tanky and destroy the enemy team
Very good at stealing the enemy minor camps
Many Escape Abilities
Ranged Ganking Tool
Great at backdooring towers
One of the best junglers at farming
Good at recovering if you mess up

Cons :

Pretty Squishy early on
Not the best duelist
Weak ganking compared to other junglers
No stun or slow

Mark of Alacrity - I choose these runes because basically anybody with little experience in the jungle could clear fast with these. If you want a more advanced route you could you Armor Pen Marks.

Seal of Resilience - Basically needed on most junglers. This gives you the armor buff that you will need to defend off the constant bashing of golems and lizards.

Glyph of Alacrity - Same as the Marks, it helps your clearing speed and sustain.

Movement Speed Quints - Who doesn't like moving like a racecar?


Possible other runes -
Marks of Desolation
Attack Damage Marks
Glyphs of Shielding
Armor Pen Quints

Wriggles Lantern : A key item for most junglers, you'll need it on Yi.
Infinity Edge : The main item for any AD carry, which Yi is classified under unless you're playing him tanky dps, in which you'll eventually get this item anyway.
Frozen Hammer : For some extra survivability in teamfights, and for that beautiful slow that Yi desperately needs when chasing down enemies.
Warmogs : If you want your Yi a Tanky beast, go ahead and get this item.
Atmas : A key part of the Atmogs build, if you get Warmogs, you'll need this item.
Bloodthirster : Who doesn't love lifesteal and tons of damage?
Phantom Dancer : Movement speed, attack speed, all on one item? I think yes.
WHEN TO GO TANKY MASTER YI
-I usually go tanky dps Master Yi because it's my favorite playstyle, but if you know the game is going to drag on for a while and you're going to need to be tanky because your team doesnt have too much survivability, you can try out tanky Yi.

These are basic jungle masteries for most offensive junglers. If you want a more advanced route, you can put 21/0/9, grabbing the movement speed in the utility tree.

Glass Cannon Jungle Yi -
Smite -
You'll want smite on every jungler as it assists your clearing greatly, and it will help you recover in case of a fatal mistake.
Exhaust -
Exhaust will assist in your ganking, which you will definitely need to do to finish off your build and help your lanes win.

Tanky DPS Jungle Yi -
Flash -
You'll most likely be bullying the enemy jungler, you'll need an escape in case they trap you.

Other Spells
Cleanse - For teams with heavy stuns.
Ghost - If you prefer ghost over flash.
Ignite - Who knows.

Play Video
Wolves - Blue - Wraiths - Wolves - Red - Golems

Other Paths -
Wraiths - Red - Golems - Wraiths - Wolves - Blue

In conclusion, Jungle Yi is a very viable jungler pick if you know that you're going to be able to farm and get fed. A fed yi will dominate in any game, and leave the team baffled as their towers drop from full to 0 in a matter of seconds. Although he doesn't have many ganking tools, he can pull off successful ganks, especially with exhaust. And any ganks can leave a tower open for a potential beatdown. From a built in AoE smite, to the attack speed buff of gods, Jungle Yi is definitely somebody you should try out.