I've played jungle yi for a while now. Tried a bunch of different builds, and this one seems to be the most successful time and time again. I originally had dodge runes, but with the recent change, I switched to armor instead.

This is possibly the most key part to any build for a jungle Master Yi. From playing him so much, I would realize i'd always get exhausted, stunned, etc during team fights and ganks. When Master Yi gets exhausted, he is completely useless, and rather than going QSS, I get cleanse instead, so my item build can focus on damage, critical strike, and attack speed. It actually works out really well early game also before the team fights, because most of the time when you're ganking, the enemy forces are on the retreat, and try to exhaust to save themselves.

With my mastery set-up, you will never really have to leave the jungle. The extra damage and return damage help out a lot, especially early on. I don't use havoc because I believe I'd rather have more armor pen and life steal, rather then 1-3 more damage on non-crit attacks.

Usually when I lane Master Yi, I will max Wuju Style first for last hitting, but because I'm jungle, I like maxing alpha strike first for two reasons. One, it will increase the chances to proc jungle to make it easier. Two, on your first couple ganks, the enemy is usually running, and you may only get 2-3 hits on average before total by the time he uses flash/gets back to tower. Rather than having some extra damage per attack, I found it's better to have a stronger alpha strike nuke. Also, another key part of alpha first is when you hit level 6. When you ultimate and kill a hero, all your spells refresh. This being said, Alpha acts as a great nuke for picking up double kills early. Without maxing it first, when your skills refresh, you really don't receive that much of a dps bonus since Wuju Style is probably still activated anyways.

To be honest, I haven't done much experimenting with my rune build. It's just what I've used, and it works. The magic res/armor runes make up for not having many defense/health items. Armor pen marks are obvious. I get the +dmg runes mainly for early jungle, and early ganks. The extra damage is sometimes all you need, which will help with your early game farm. The health quint is to have a bit more survivability.

Having vampiric scepter allows you to never have to leave jungle using my route I illustrate below. The rest is standard up until the ghostblade vs phantom dancer argument. Although they are very similar, I find the added damage and armor pen of ghostblade to be better earlier on then phantom dancer. There are also two reasons for this. Since it is jungle yi, he's primarily in the jungle unless he's ganking. Ganks shouldn't last that long, so the added attk/move speed bonus of ghostblade should suffice. Secondly, the added damage and armor pen makes Enemy champions drop even faster. Especially because at low level, each point of armor represents a huge proportion of damage reduction.

Edit: Also, the cd reduction of ghostblade helps when chasing and you need alpha strike to be refreshed asap.

This Jungle pattern will allow you to clear the whole jungle at about the 4 minute mark. It could be a bit faster / slower depending on crit/alpha proc luck.

Here's the order of your first round:

Leashed Blue (Smite blue)
Dogs
Wraiths
2 Golems (Make sure NOT to use smite here)
Red (Smite Red)
Wriaths (By time red is done and you run over to wraith spots, they will be refreshed)

By now, you should be level 4 with life ranging from ~35%-full(Full only if u get super lucky with alphas and crits)

From here, I check paths for a low enemy champion to gank. If health is too low, you can just Back. You should be able to dragon when you have beserkers, wriggles, and avarice blade (unless of course team is willing to help, then just wriggles).

Pros: This build is very Early/Mid game build. You will be VERRRRRY powerful in this range, so make sure to gank often and push towers after successful ganks.

Cons: You dont have too much health, and you tend to be a bit squishy. Make sure your tank initiates in team fights, when they do happen. Be ready to cleanse when you get stunned /exhausted. Part of Yi's survivability in team fight is his alpha strike. When you kill a hero, instantly alpha again in team fight, because most likely, their whole team will be aiming you.

When vsing karthas, make sure to get a point in meditate at a lower level.

When vsing warwick, Malzahar, and Skarner, you may need to get a QSS on top of having your cleanse since cleanse currently doesn't stop suppress abilities.

When I go to kill a tower and it looks like the enemy team may be there shortly, I make sure to save my ult, and use ghostblade instead. Then, I can highlander away without worry of getting slowed, etc...

(When you have highlander and ghostblade)
If you are running away from an enemy hero, burn these two spells back to back rather then at the same time (Unless you are right next to the enemy and must escape asap). By doing so, in the off chance you get stunned, it won't take time away from both highlander and ghostblade's speed increase. Also, you may only need to burn one of them in the first place to get away.

The key to team fights is you MUST get the last hit for all your spells to get refreshed. This becomes VERY key as alpha getting refreshed mid-fight could turn a losing fight into a winning one. The 1200 dmg nuke (lvl 5x 4targets) plus being able to highlander again proves to be powerful.

Because of the above, you will want to target their weak champions first. In team fights, soraka, sona, fiddle, caitlyn, ashe, etc are all good targets. Mainly weak support, caster, and carries.