For the second item buy you either pick between cutlass or wriggles. cutlass for more requested ganks and more damage. wriggles lantern if your teamates are winning there lanes so you can just super farm and snowball ahead of the rest. just never stop killing anything. DO NOT buy the wriggles lantern if your teamates lanes are losing or if you feel as if there about to lose a tower because than you wont be able to upgrade it to feral fire since the meta game will be coming alot sooner and you will have to be split pushing by than and a non upgraded wriggles lantern is just the worst thing to have by than instead of a cutlass which can slow down enemies for escape or to finish a kill.

Okay so the reason why this build starts out with attack speed and damage is so that you can snowball. either by farming so fast your just ahead or clearing waves and split pushing killing towers or ganking. teleport is for ganking split pushing or to save a tower. after youve snowballed to get your first two main damage items it will probably be meta game by than so you should focus on split pushing, clearing waves fast with your atk speed and damage and getting towers down and also focus on lone enemies. i believe you can face anyone 1v1 with yi and beat them unless if there fed already. so after you get thornmail you can start hunting anyone except there apcarry since you just do so much damage and food armor. in teamfights you still want to wait a bit to engage but focus on killing there ap carry since you dont have any magic resist yet and after there dead you can take on there ad carry or jungler fairly easy since you have armor. towards the lategame you will need more health and armor for your teamfight viability and split pushing so i think randuins is perfect. there adcarry and jungler if there are also a heavy ad bruiser wont be able to 3-4 shot you. you will basically be able to kill anyone 1v1 with ease except there ap carry but usually if there ap you just have to dodge there skills or w when they use there skills unless if its leblanc than thats tough lol but still can be done! with katarina just run away from the range than run back but make sure you ss so you can go run away from range than come back within range in time :). so if the game is still going go ahead and pick up spirit visage. usually since you snowball with this build you can get these items fairly quickly. now with spirits visage you will have about 2800 hp with around 280-300 armor i think and about 100-120 magic resist if i can remember correctly. and you do 300-400 damage per attack and you attack twice per second with spirit visage you have 40% lifesteal and 20% spellvamp. with 600-800 damage (hybrid damage) your basically healing yourself about 120-200 per second. if the ap carry cannot one combo shot you than there pretty much in trouble. dodging skill shots and using w at the right time is essential for late game against ap carries.