Hey guys! I'm a Master Yi main who has been playing league since mid season 2. When I first started playing ranked I did have a set main role or champion and kept teetering around silver 1 not being able to settle into a role/champ that felt right. Then came Master Yi. In season 3 I sat down and started playing Yi because I liked his "In your face" damage and his ability to mow down towers in a matter of seconds. In no time at all it seemed like I blew through gold and I'm now teetering around the plat 1 D5 range. But that being said I wasn't a prodigy Yi player, it took me many many games to finally settle on what to max, what to buy and when, and most importantly how to clear camps efficiently.
My goal with this guide was to not just give a cookie cutter "This is what I do for runes and masteries etc. guide" but to instead make a guide for someone who may not even know how to jungle or hasn't done it alot to be able to read this and not only get a great handle on how to play Yi, but at the same also teach in depth jungle play style tips that can carry over to any other jungler you may decide to play as well.

So unlike most other champions who have many different variations of rune pages to choose from Yi has more of a one size fits all rune page which in itself has its fair share of pros and cons.
First off Yi's main stat for the Devourer playstyle is of course attack speed. Essentially you want to have close to the 2.5 attack speed threshold with your ult up late game while only having your two attack speed items; Bork and Devourer. (I don't include attack speed boots because you won't be building them every game like you will Bork and Dev)so that being said you need to cram all of your primary attack runes (Reds,Quints) with attack spend netting a solid ~29% attack speed steroid right off the bat. This helps immensely early on with clearing camps making your q CD lower and allowing you to apply the krugs buff more frequently.
The Yellows are there specifically to help keep you alive in the jungle early and survive early skirmishes should you get in one with the mix of armor and hp. (Even ap champs do more physical damage than magic damage with their auto attacks pre level 4)
And now on to blues. This is the only spot on your rune page where you can be semi flexible. Typically i choose to forgo MR and just go with the 5% cdr early and scaling 5% cdr late game so i always end up with at least 10% cdr no matter what i decide to build. Though if the team is extremely ap heavy you can opt to add MR here instead of the cdr but youll have to be aware of your longer cds because of it. Again personally I just prefer to take the cdr and try to outplay my opponent instead of just eating the damage but that decision is completely up to you.

Nothing that needs too much explaining here. Just a standard attack speed based ad jungle page.

Here's where yi actually shines as an assassin in my eyes. He can be more flexible with his builds than any other melee assassin the game ( ARGUABLY of course, AD fizz is also quite flexible as well as rengar). Being an assassin that runs off of just 2 core items he can either from there transition to a full assassin or an off tank or more a of bruiser all based on what you need to be for your team that game. Having such a high base damage as well as insane scaling with the attack speed stat makes it to where you can easily kill any ap or ad carry with only a bork and devourer in a matter of seconds. But as most of you know yi has difficulty surviving in team fights from the high damage coming in from the enemy team and cc, but what if I told you that could be easily worked around?
Since you only need 2 damage items to be a relevant threat to EVERYONE on their team you can (and in most cases should) make the rest of your items from that point on defensive and here is why. No whats scarier coming at you in your mind: 1. A Yi coming at you with full damage that can probably more or less two shot you but can be out played with cc or high burst damage or 2. A Yi coming at you with 3k plus hp good armor and mr and can still kill you with virtually no window of being out played? (generally if you cant solo a carry its because you made a mistake) I could go on in this section of the guide for hours so ill try to wrap this up.
Tldr; stacking defensive items on yi after his core damage items makes him a massive threat to the enemy team. Examples would be randuins, thornmail, tabi etc. vs ad and spirit visage, banshees, maw of malmortius etc vs ap. Also worth noting frozen mallet is almost always a good pick up in most games unless you need to stack resistances (like playing matches vs 4 ad champs or 4 ap). Ultimately the way you decide to build Yi heavily impacts how you will perform in the game.

Nothing that needs too much explaining here. Start q for the clear speed obviously and w second for the sustain in the jungle. Take q again level 3 because your e early game doesn't really give you much in terms of clear speed or overall damage and can easily be put off until level 4 or even 5 in some cases but it is important to have it at 6 for your ultimate. then its just a standard max q max w max e path.

Typically, you're going to always want to go teleport and smite. Taking another spell over tp just gives up almost all of your split push pressure and makes you have no global presence.
Teleport: The reason why this is your go to spell instead of flash or ghost or something else is basically for the map pressure. As you know yi isn't exactly known for his early game presence or cross map mobility. And thats where this nifty spell comes in. Early game you can use this spell to tp in and help turn around a gank on your teammates or even flip a 1v1 or 2v2 in their favor by tping to the enemys escape path or just far enough be hind them to where you can catch up to them even if there are multiple ways for them to run. mid to late game you can do the same as you were doing early game but also now gain more opportunities to use the spell. Now you can split push freely without worring about the enemy team swinging objectives on you, though you still need to watch for them running to get YOU of course. Also you now have the option to do the very fun TP backdoor strategy if your team gets caught out or if you just see an opportunity where you can get a tower/inhib or even the nexus faster than they can move to stop you.

This isn't too complicated thanks to your Q. Basically you always save your smite for krugs if at all possible or gromp depending on which side you start your clearing each time you go back to the jungle. Though if you are afraid of getting counter jungled by an aggressive jungler smiting wolves or raptors for the vision is always a good option. Now for actually clearing the camps it basically comes down to if you want to clear the camp fast or efficiently (losing less hp). For a fast clear just keep autoing the largest monster in the camp and spam q whenever its up. Also, and this applies to both methods, always wait to activate your e until your passive is about to come up to guarantee you get 2 double strikes while your e is active. For a slower clear but more HP efficient process, auto the small camps down first before the large camp. This method is parasitically useful on the raptor camp as the 3 small camps do as much damage as the large camp.

Decided to separate this from the jungling section to make it less cluttered. So typically this only applies when you're farming out your sated devourer other wise just disregard this and go to whatever side of the map you're wanting to pressure. So as soon as you get your devourer you're going to want to start power farming camps and looking for ganks and hopefully a dragon. If at all possible I recommend starting and krugs and working your way up or down your side of the jungle from their assuming one of your buffs aren't up. Also check the river for scuttle crab between your camps to heal up and try to pick up the two stacks you get from killing him, just be weary of the enemy jungle and laners collapsing on you in the river. asides from that if you can't or dont want to start krugs or that area isnt safe at the time just start gromp and work your way down to krugs. The 4 regular camps will give you 4 stacks and each scuttle crab will give you 2 a piece.
Very important to note that dragon and baron both give 5 stacks which is absolutely insane seeing as you only need 30 total. Very important to secure one of those objectives early if at all possible to get your devourer sated as fast as possible. This all being said though you are still a jungler and do need to help your team even if it cuts into your stacking a little bit. You're a jungler first and a late game hyper carry second :P