Hello!
This is my first guide so please leave comments on how to make it better.

This is how i usually build Master yi but i don't say it will always work. But in most normal games it does.

Pros:
- Very fast even without atkspd. items due to his ulti.
- He can be played in many ways, he is a good AP tank too with the help of his meditate.
- You can deal tons of damage with him
- he takes away the most common cc, slow, with his ulti and can escape fights with it too.
- can use his ulti over and over if you have blue buff and keep killing enemies.

Cons:
- Rather squishy early game
- He's probably dead if someone hit you with other cc's than slow.
- The items he need to be awesome are very expensive.

As you can see there are more pros than cons and the cons he have are only minor problems that are easily solved.

There is not much to say about the masteries. He is an AD carry afer all, but if you for some reason would like more durability you can put those 9 points from utility and put them in defense. I also took the utility mastery so i wont have to buy a slowing item but i can get the red buff instead and keep it until it comes back.

The same goes with the runes but i have already done that because i dont think he'll ever need more defense than that.
I took pure ad marks for a better early game and easier farming.

With this item build you can take out most champions in maximum 10 sec as i said in the build name you get over 1500 crit 57% of your hits and with 2.5 attacks/sec you can give them hell of a lot damage.

I get Tiamat as the second item because it gives splash damage and therefore better farming but i sell it in late game and buy somthing more useful instead like the other bloodthirster or a last whisper, it depends on the game. But if you are facing a noob team with no tank you really should keep it to pwn all of them at the same time in teamfights, especially if there are more melee champs than ranged.

If someone get thornmail in lategame it's best to switch the black cleaver for another bloodthirster to get more lifesteal than the thornmails damage to you.

And. if the other team are only squishies you should get madreds bloodrazors or another bloodthirster instead of last whisper because the cleaver will give you all the armor pen. you'll ever need.

I don't get more than two attackspeed items because if i did his ulti will be wasted on nothing but movementspeed because you can't get more than 2.5 atkspd. even with his ulti activated.

The core items of this build are Phantom dancer, Infinity edge and Bloodthirster. The boots can be switched with something like mercury treads or boots of swiftness for cc reduction or more movement speed. You should switch all other items depending on how the game goes.

I've chosen flash and exhaust because both can be used as offense and defense and i dont want to waste an item slot on a slowing item like frozen mallet because it doesn't give any significant damage. So i get the red buff to slow with my attacks as i said in the mastery chapter.

If you want to avoid cc you can take cleanse instead of ignite because the only cc he can avoid is slows. but things like stuns and lock ins from opponents like annie, morgana and lux can kill you if they have built their champion right so they can deal heavy damage to you.

Ignite is mostly used to finish off low health opponents early game and prevent healing during the whole game.

I don't have a skill sequense that i use all the time because i can't remember it but i always make sure to max wuju style first for the damage boost. But i start with alpha strike for farming. Meditate is better to max befor alpha strike because it can keep you alive if you are being chased, just run into some brush and use it becaus at max level it give 300 armor and magic resist.

It should be pretty easy to farm with alpha strike in early game but if you have laningopponents that harass you all the time you should go jungling sometimes in mid-game to get xp and gold.
otherwise you should only get the red buff when you don't have it.

This is all i have to say about Yi and i think he is a really good champion as a first champion.
And he's too awesome because you dont need to buy so many attackspeed items but instead go for pure damage and still get 2,5 attackspeed.