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v2 - a couple of chapters rambling on about what the difference between what I mean and what most playerse today mean by backdooring.

Poor old master yi. Loved by all, but he simply doesn't hack it at high elo. For July - August 2012, over at http://www.lolking.net/, based on results, he was statistically ranked 3rd worst champion after Karma and Evelyn. That's out of nearly 100 champs.
That's pretty bad.

What to do?
Besides waiting for Riot to buff him, we can try always different ways of playing him and building him.

Well, this guide describes an old way of playing him, but taken to a new extreme of building him.
Give it a try!

Long ago, their was a tactic that broke summoners rift. A champion would take down several turrets, one after the other, away from the main battle, without any help of any other champion and without friendly minions to soak up the turret hits.
It was called backdooring.
The high overlords of the league were displeased with this ignoble evasion of battlefield justice, and so they greatly empowered turrets, so that while no enemy minions were near, the turrets were too strong to be soloed.
The tactic disappeared from the league.
But the term 'backdooring' didn't.
Instead summoners began casually referring to pushing top and bot lanes while there was a team battle at mid as 'backdooring'.
This causual reference caught on, and new summoners these days use the term backdooring without ever knowing what it originally meant, or how it used to break summoners rift.

The threat of a backdoorer is simple. A team facing a very strong backdoorer cannot leave their turrets unguarded for long.

If you are playing as a backdoorer, your job is to punish the enemy from taking anytime away from his turret.
This can be a shocking threat to most players today.

Why?

These days there is a rule that is almost set in stone
- Your turret is safe from solo attacks as long as the creep front is advanced well infront of the turret.

Every summoner today lives by this rule, whether they consciously know it or not.
Take mid for e.g.
During the laning phase, mid's like to gank bot and top with their high burst damage.
So to do this, they push the creep wave at mid to give themselves a time window to get to the other lane, gank, and then return before the creep wave is pushed back to their turret.

This is done many times in every game.
It's a rule that every player uses so often, some don't even think about it.

But wouldn't it shock the heck out of the laner, if when he came back from his gank, he found his turret destroyed, but the minion wave had not pushed it?

What the hell just happened?

You've just been back doored, old style.

That's simply what we're aiming to do. To push every mastery, rune, item, summoners, ability, and team strategy towards creating the League's ultimate backdoorer.
And I don't mean neo-backdooring aka pushing top or bot while there's a team fight at mid.
I mean old backdooring - taking a turret solo while your minions and your allies are elsewhere.

Let's get on with it.

Critical strike doesn't work on turrets
- Items like infinity edge and phantom dancer are far from ideal

Armor penetration doesn't work on turrets
- The usual armor penetration runes, masteries and items are rejected

Magic damage off items doesn't work on turrets
- No wit's end, malady or madreds blood razor

No life steal off turrets
- so life steal isn't that usful

So what's left for us to focus our build on?

Attack :
Straight AD damage, Straight attack speed

Defence :
Amour , Health


Turrets : are worth 2.5 kills. If you have to die to take down a turret, all other things being equal, its worth it just for the cash. Do it.

Turrets : destroyed wins games harder than champion kills. We've all played plenty of games where our team has been 15 or more kills up and still lost. What went wrong? No amount of kills will secure a game. But a team only has 11 Turrets, when they are gone, their winning chances are very slim.
Even if the cash incentive wasn't there, they are still worth one death to destroy for this reason.

If you see you are getting inescapably ganked, like all your escapes are on CD, or they've simply got u surrounded, their is one option which a new Back door player might not consider -
Dying to the turret ! Letting the turret kill you is not nice, but its a heck of a lot better than dying to a champ!

If our Yi is going to be pre-occupied with back-dooring top and bot lanes, it's pretty much a given he's going to be pushing them as well. i.e. he'll simply progress from being a pusher into a backdoorer when he's got his build up.

Remember, you are not the primary farmer on your team. The AD and AP carries should take a decent share of the farms throughout the game.
This means doing some backdoor where pretty much any other champ would take a farm and push the lane.

Don't go in with the expectation on yourself of BDing a full health turret in one go. That's unrealistic until full build. If you can take half a turrets health, then its a job well done in nearly all cases.
Even a third is OK. Any less than that and you need to build up more.

Take leveling AD Marks, armour Seals, and AD quintessences.
The reason is simple. Backdooring and pushing becomes more tenable as the game progresses, that extra damage and amour over flat runes will be helping our plan.

For glyphs, this build is a lot more flexible.

Flat magic resistance glyphs are a standard, sensible choice.

But also consider -
Master Yi's meditate scales superbly with ability power. This justifies taking ability power runes, flat or leveling. Meditate is an important part of master yi back door strategy.

Mana regen gives a major boost to your sustainability in lane thru meditate. Consider it for tough lanes that are draining your health.

Yep its a odd tree.
We are trying something different, so its odd.
This is what a mastery tree looks like when it's optimized for backdooring!
It's pretty self explanatory, study it yourself and convince yourself its ideal for what we are trying to do.

Notes :
- Weapons expertise, the 10% amour penetration mastery is taken, simply because that amount of amour Pen for 1 mastery point is simply too good to neglect.

R ( highlander ) and E ( wuju style ) should be maxed 1st. It's AD and AS, vital for the cause.

For Q ( alpha strike ) and W ( meditate ) there is no set priority.
Alpha strike is not important for backdooring, but it's useful for pushing and lane harass.
But bear in mind
- you'll need at least a couple of points in meditate to tank the turret shot you didn't quite run away from in time.
- when you aren't strong enough to take down a turret in one go, one tactic available to you is to back off, meditate, then return for a few more hits. Your wuju style will be back up by the time you return. So for this, the more points in meditate, the better.

Teleport :
This absolutely core to a backdoor strategy.
You are going to place wards in advanced positions, to which you can teleport to and move in to attack turrets.

Ghost :
This is a desperate escape spell for when you dont have time to recall and highlander is on cool down.

Spells not used :
Exhaust : This works as an escape, but only against 1 enemy. If there's 2 or more, its much less useful. For escape from multiple enemys, ghost has a distinct edge over exhaust.

The items for this build just look wrong.

But they aren't.

This is the build you come up with when you try an all in anti turret build with advanced and lengendary items!
My first thought was that the leagues items are simply not designed for specialization in turret attacks. In fact I wonder if riot has counter engineered the items to dissuade players from going for anti turret \ back door builds.
In short its seems difficult to come up with an anti turret build while optimizing 6 item slots, but this is optimal and I'm happy with it.

Lets consider what anti turret specs these items give us.
Insane AS - 155% extra attack speed!
Modest AD - 78 extra AD
Decent health - 500 extra
High amour - 130 extra

Aren't we lacking in AD ?
NO! Wuju style, our leveling AD runes, our masteries, and Yi's decent AD base provide the rest of a sufficient AD.

Ok, but why not balance it out with a bit less AS and a bit more AD?
Because wuju style active time is clutch. Once activated, you've got to get in as many hits as possible, and you dont get much time.

Hey! AS is useless without AD!
- I know where your coming from. We've all seen novice AD carries taking AS items and few AD items. They can't do deal decent damage to enemy champs.
But...
The same doesn't apply for attacking turrets.
Straight AS is more effective against turrets than it is against enemey champs.
Why?
Well, a significant part of the damage from straight AD items is due to the armour penetration of AD carries. ( all good player know to take last whisper as their 2nd advanced AD item , for its armour pen, its effective damage is better than a bloodthrister! )
This just doesn't apply to turrets. Turrets ignore armour pen. So you can build AS and reap pretty much optimal scaling turret damage with it. Do it.

As for high armour, this is more important than health. Health is what you get when you don't know if you are facing magic damage or AD damage ( or true damage ). We know we are facing AD damage from turrets, so we get more amour.

And a really big thing about this build,

IT IS VERY CHEAP !
really. So cheap. I reckon this build is at around 3000 - 3500 gold cheaper than a typical AD carry build.

But it gets better.

Because the league's items seem to designed against pushing turrets, the optimal items for us are actually basic items, and you get these early. Really. Let me explain...
Take the Black Cleaver for e.g. Seems like the right item for the job.
Cost 2865g, AS = 30% , AD = 55
But check this out...

Recurve bow cost 1050, AS = 40 %
BF sword cost 1650, 45 AD
total cost 2700g

You actually get pretty much the same anti turret spec from these 2 basic items combined than from the black cleaver, and they cost less.

This means your relative turret pushing skills will seem to improve fastest mid game.

You already know how good yi is pushing turrets with his conventional items... just imagine whats gonna happen with these items...

But seriously, so much AS?
- Yep. Another thing it comes done to is that AS items are generally cheaper than AD items.

OK,
That's serveral good reasons to have high AS. Just get on with it. You'll see.

But that said, I've got to mention...

Alternative items : these typically replace the 2nd ionic spark

- tiamat

Yep. Seriously. No REALLY.
Extreme Backdoor master yi is the leagues most dedicated BDer and lane pusher.
How many times have you heard people say tiamat is one of the most cost efficient AD damage items? That's because its true. But it fails to get put in builds because other items are just ... better.
But for what?
Fighting enemy champs.
We aren't doing that.
Anyone who is fighting enemy champs should take bloodthister over tiamat. But the excellent life steal on bloodthrister is wasted on turrets.
Also, tiamat is excellent for lane pushing.

Many master yi's think they are awesome lane pushers, but the truth is, yi is not a top tier creep pusher. Not quite. Kayle ( for 1 ) pushes faster. Tiamat's passive brings yi into the top tier of pushers, and it's a cost effective anti turret item.
Minor bonus : Tiamat replaces the mana regen we lost when we sold our dorans ring. A bit of mana regen on yi is useful.

You are weak !

We aren't looking to squash the enemy laner, we aren't built to do so.
You are just looking to survive and farm.
A point in alpha strike, a point in wuju and a couple of points in meditate should be a safe start.

Play as safe as you can, and ask you jungler to do the work of subduing your opponent with some ganks.

mid game starts when a turret goes down somewhere on the map. ( or perhaps when the whole team 1st converges on dragon ). The key thing is team fights are starting.
Master yi is not a good team fighter, and with this build, he's even worse!

Stay away from team fights, or at least stay on the periphery and only engage when its really safe to do so ( you coward ).

But the whole point of this build _is_ to be away from team fights. As far away as possible, because this is your chance to start phase 1 of your special skill - pushing!
Pushing needs no explaination, just kill all the minions get your creeps to the enemy tower.
Attack the tower with auto attacks and any enemy creeps around the tower with alpha strike.

Wuju style
- Time the use of this skill so that it ends just as your window for attacking the turret ( or even the minion wave in poor cases ) ends. Activated too early, and your left with low power attacks. Too late and you've wasted your E as your running back and not autoattacking anything.

Team strategy
By now your team should know what your up to. Often from teams that don't know what you are doing there are calls and pings for u to join in the team fights. For most cases, you're not going to team fight.
A team that understands what you are doing should team fight defensively around their own turrets.
If all goes well, the enemy team won't be able to break thru 5v4+turret, so will have to back off due to you pushing a lane.

In late game, a 5v4+turret usually goes the way of the 5. The turret is simply not strong enough to make up for a missing champ. For our purposes, this is what defines late game from mid game.

As a lane pusher away from the team fights you have to compensate for this by -
Being able to solo down turrets faster than the enemy can destroy turret in a 5v4 team fight.

Again you are depending on a team that understands this, and are prepared to forfeit kills and turrets at a managable rate, and will trust your solo pushing to compensate.

Again if all goes well, the enemy team will have to fall back to stop you, allowing your team to apply pressure mid lane.

Wards wards and more wards.
You keep your wriggle's lantern all the way to the end, not least for its ward.
Wards prevent ganks in the early game laning phase.
Buy a ward everytime you go back mid game ( on top of your wriggles ward).
Mid game when the pushing starts they show where the enemy is ( and more importantly for us, where he isn't ! ).
Get wards next to each outpost enemy turret so to prevent getting ganked while you attack it, and also so you can teleport right next to it for a fast turret take down.
Ask the team support to advance the placement of his wards for your purpose.

Pros
- unique build and strategy, no one is expecting pushing and backdooring this extreme!
- ( very? ) cheap build
- helps for jungle yi that its cheap
- should work for jungle and top lane yi

Cons
- requires and understanding team
- weak early game

Some time late game you are going to be able to start backdooring for real. That is - taking out turrets without your minions around.
This typically won't happen until you get to the thornmail item, and then it'll still be taking everything you've got ( solo back dooring is damaging, even for the best backdoorer with the optimized build ! ).
But there are few things that help us in this situation.
- in mid and late game, enemies don't tend to hang around, or travel past, top and bottom turrets when the creep wave is advanced. Or at least they won't do it in numbers, and you can escape from 1 enemy champ.
This is gives a natural opportunity for backdooring.


When a turret has beaten you and you have to back off - meditate a safe distance and then return to attack again. When enemies see you back off with little health they sometimes assume the immediate back door danger has passed. It is a pain for them to have to break off their team fight to deal with you, so they might want to believe you've retreated.
Of course hanging around repeat backdooring the same turret requires high map awareness and ward useage.

- a lot of the time you won't have to backdoor a full health turret. You've already damaged it during the pushing phase! Low health turrets are no problem for extreme BD yi.

- mix up your activity, i.e. pushing, and your BDing, and normal yi stuff like jungle and stealing jungle. This adds a bit of randomness with which to throw off the enemy.