This breaks all meta and is only for experimentation, this build is a work in progress. This will not explain everything, only things that break meta will be explained. The whole point of this is to do "shock and awe" there is nothing worse than a guy who counters your AD, and swings at max speed... its overwhelming, and to add insult to injury, you cant escape him because he is so mobile, has some reach and fast movement speed. 435 is plenty but if you find yourself against a Singed or Teemo, you might try the boots of mobility or swiftness to chase them down. Again this is not a practical guide, this is strictly situational, but if you break meta its either going to work or fail, depending on the counters, the team, the player, and luck. Not a competitive build, but like i said, is for shock and awe. You jump on them hitting as fast as possible, their first reaction is often to run, and you can out run them. The goal here is that by the time they figure this out they try and engage, but its too late. more explained in the items section.

PRO's

Fast attack and Decent damage per hit = high DPS... i call it shock and awe... it works.
fast and mobile, easy to chase down anyone
solo lane farm fast
great jungle, save money on potions
Has a nice poke for a melee champs

CONS's

Squishy
End Game build, weak at the beginning.

NOT TESTED NOT RECOMMENDED AT THIS POINT

All AS except the Glyphs, the .6% gain on glyphs isn't worth the slots, besides, you don't want to waste cap speed.... and so i added magic resists, pretty common glyph.

This is pretty basic, i went with 21-9 AP route and grabbed the AS pieces. This is a heavy AS build focusing on AP, I will add an AD build soon though too. I did get the health masteries because your not going to be very tanky, so every little bit helps.

Shard of True Ice
I like the idea of building this first for the extra gold, and it gives a little early AP, the Aura is not needed at all, but is just a bonus. This is an assassin build, so your likely in jungle or solo top, your going to wander and get the ganks, so you might lose some CS farm, this will counter that effect. If you do manage to farm well, this item added will get your expensive build much quicker, and anyone knows, GOLD WINS GAMES so get this first and fast.

Berserker's Greaves
If your solo top with a teemo or singed, this might be a better first pick if you see they are out maneuvering you. You must get out of range from teemo's pokes and stay ahead of singed. If speed isnt a problem early on then wait to build this second. get the boots of speed early, but finish this item second.

Malady
Only a little more AP right here, but a nice gain in AS, plus im a huge fan of passives over actives, if i can help it, its always on so its always effective. This gives you bonus 15 damage to basic attack (your main weapon with an AS build) +10% of your AP. we will be sitting at around 400 AP end game so that will be a 55 bonus to each hit... if you hit as fast as possible your going to be doing doing about 143 more damage per second with just this passive. Totally worth it for just over 2k gold!

Nashor's Tooth
2200 gold gives you a nice boost to AP and huge AS, with a bonus 20% CDR so thats nice, i think this is a great value even without the CDR, this is a perfect weapon for ASAP Yi. This build is mainly Attack Speed and Attack Power, so this has both and then the CDR is good for anyone. In fact i would recommend that you use CDR Glyphs IF (and only if) your going to get rid of Magic Resist... but thats just me.

Rabadon's Deathcap
So this gives us 120 AP, at this point were not worried about AS anymore, we just want to make his attacks hurt now, and with the passive (love passives) it gives +30% AP, so that give this item 156 not 120... and its added to your total AP not just this item alone, so at 400 AP with a 30% (passive) boost, this passive is like wearing 2 Rabadon's (another 120 AP from this passive).

Rylai's Crystal Scepter
At this point, if the game is still going, your going to want to drop your Shards of True Ice, and pick this up. It adds a large amount of AP, and thats nice, but whats better is the 500 more health and yet another passive :-) of slowing down your enemies when you use your spells... by 15-35% (depending on multi enemy spells) for 1.5 seconds. so if it wasn't bad enough that they cant out run you, when you hit them with any spell, your slowing them down some more, and thats fantastic. Of course use your brain, if your getting ganked too easy by end game and need to be more tanky, then get a Warmog's for more health or Thornmail if getting hit up by a Teemo or someone who is basic attack heavy.

Firstly, this AS build means that Yi's passive (double strike) will proc more often making it more effective passive, and you know how i like my passives.

The ability sequence is pretty standard, its meta for sure so i dont think i need to explain this to you, but you want Q first because of the farm and the reach out and touch someone poke it give, which is nice when your not a ranged attack. W is great because it saves alot of money on pots, this skill is why we go AP (and other reasons) but the 400 AP you have makes this skill (when full level) restore 1600 health in 5 seconds, and lets not forget the added 300 armor and magic resist, making you invincible for 5 seconds. its like 2 Zhonyas or Wooglets but it heals you instead of nothing. Since we will have a Wooglets, were talking about 7.5 seconds of survivability that heals 1600 health and thats like another life right there, making you very valuable in team fights, sine they will PROBABLY focus you first or second and this can mean an ace on your team if you stay alive for that long, its a game winning combo.

E is almost useless, and is more for a AD build so don't worry about this as much, and remember when you use it, it takes away your passive while on CD, which isn't particularly short, so try not to use it too much, it will actually make you weaker in this build.

R is an awesome ULT... this is not needed as much for movement speed or attack speed, since we built for both these things, allowing you to save the ULT for when you really need it, ANTI CC... it will get you out of anything that affects your movement speed, and this means breaking their ULT's usually... so this can mean LIFE and not DEATH for you, and the other way around for them. SAVE this for when they try and do a team fight and want to focus you, just use the ults if they are going to CC you, then when the healh is low use the W and your Wooglets and they are aced... GG

Pick what your best with, but gotta have a flash no matter what, the other is up to you, but i recommend smite for jungler (obviously) teleport for general messing with people and being global assassin in seconds (insta ganks) Ignite for getting the kill without having to turret dive and getting killed (since this isn't a tanky build) Other than that its up to you, but i recommend those as your second spells.