Hi every one , this is my first guide, I thought I'd share with people how I play Diana and I do insane damage with her. Let me tell you this guide is different from any other you've seen and it ain't the way most pro players would play, but hey I have so much fun on her with this build that you should give it a try too :)

P.s I started to try this build after knowing about the abyssal scepter rework. Some people say lets cross the river once we'll be there. I build a boat cause i know there's no bridge waiting for me ( like that gap when Rito removed dfg )

Important parts are runes masteries itemization and tips and combo will help you to get the best of Diana's kit.

15/15 ; half magic pen half ap, wreckless you migth say but diana got good base stats and the possibility to out trade (if you can call her combo a trade) most mid laner.
The reason I run those runes is to deal TRUE DAMAGE with my abilities and to do it fast. I use to need 2440 more gold to be at same point in game. all that money now go in a rabadon/zonyah to secure my burst.

Here's the thing, when you complete your boots you are now at 30 magic pen and most champions have 30 base magic resist. for some reason lots of people will stay at the 30 with this in mind click on champs and check there stats. they got 30 magic resist. if you can PENETRATE ALL THERE MAGIC RESIST then all your magic damage is doing to do the totality of its damage and not the 24% reduce magic damage that they have as base ( 24% of a thousand is alot of free damage gain..thats the type of damage gain we are looking here)

The problem with magic and armor pen is that it's complex math until it reach zero. But have a look lets say there is a target on a team that has 30 magic resist or close to that , having 30 magic pen will mean you will deal 24% more damage with the base stats of ability as well.
Q does 200 plus 70% ap . 200+70% lets say mid game you have 386 ap
(rab, lich,double doran ,sorcs level 16)
200 + (.70*386) = 200+270 = 470 thats the damage you deal with full penetration.the one showed in tool tip
with the 24% reduce from magic damage your q is doing
470-(470*.24 ) = 357 so a difference of 112. to reach that difference in ap you need 160 ap and thats only on one spell. Gold efficiency here we go :D

So as far as itemization go i like to go a doran 2 pot start (gives me a decent 32 ap start) , back when ever i can buy doran boots. I rush sorcerer boots for that early power spikes given by the cheap double doran+ full pen rune combo with the boots giving that 15+15 magic pen previously mentionned in the rune section.

After that i buy one sapire crystal to raise the bar the mana bar( helps alot to buy it there)
rush Rabadon in 99% of the time the only two time i rush Zhonya's instead is when my life is greatly threated by 3 of theses champions : ZED TALON AND FIZZ. Other wise no need to go Zhonya's as other mid laner like annie or malzahar for say will have cc that will even prevent you from using your zonyah. In any case after the Rabadon or Zhonya's i go toward a lich bane with the previously bought saphire crystal. this is another power spike as it will able you to get E which is a no damage ability into a lich bane proc (magic damage on AA OP since magic pen build ). you see this build focus on getting the most damage with the less gold possible. your already able to do your assasins job with only those 3 items or 7400 gold . now comes diversity : Survivability or Oppression.

You can choose a tankier set of item like Zhonya's, Rylai's, Abyssal scepter(till the rework) or Will of the ancient are all acceptable choice's Zhonya's being the better choice for survivability as it gives lots ap for your shield aror to sustain tower dive situation and the passive for your cooldown resets or getting off agro or what eva proplays you can pull up with it.

Or

You can choose the Oppression build path that i take in most case. its farely cheap and tend to finish games before being full build anyway. Nashor tooth Morelonomicon. there you go ! usualy early games item, these items when builded late game with a prior rabadon scales better and allow you to reach another power spike ( what ! arent you already powerful enough )
Taking nashor with the arcane blade mastery will able you to deal 100%of your ability power with your passive. Which half of it is applicable on turrets (recently fixed a bugged where it wasnt dealing the full damage it should have been) plus lich bane procs on turret too.
You got 3 ability to chain for your lich bane to procs on turret and thats with out any target. And then morelonomicon is for the cheap cdr you can also go will of the ancient if you know you'll have blue buffs for the fights.

40% cdr is op and I'll explain why in the TIPS and COMBO section

only note here is taking another point in w at level 4 is actually a good idea as it give you a better shield and if you land the three rotating blass on enemy champs you make up for the damage you didnt took in Q. So normaly it means you'll be safer at level 6 having two point in Q two point in W one point in E on point in R.

As far as laning goes i tend to play really agressive with diana until the 3:30 where i fall back to behind the river and keep my blue side warded. here's the tips most jungler will go for ganks after there first clear and with this in mind they will come from the red side( except lee sin and nidalee that can totaly camp you level 2)

Diana got one of the best wave clear as her two primary spell plus passive are aoe.
That being said i push hard then fall back till the jungler show somewhere then when i know he's else where I push one last time real hard taking all my pots all my mana and back most of the time forcing my enemie to back and most mid laner arent that good at early farming under tower...the 10 cs early lead can be impactfull.especailly when you force them to back with nothing to buy.
your first items are super cheap to buy but you need them early. another doran, and boots.

Then you come back keep your mana for level 6 force a trade with them don't double ult them..or yet cause at that point you wont do enough damage to annihilate them one shot. So your level 6 first burst need to be a poke then 8 second later your in for a kill. and you can safely do it under there tower unless they have some hard cc( don't go diving annie or malz ...smh) After that kill depending on how things are going you got two option or you stay or you back. Staying means your above 50% health got enough mana to do a combo and still got summoner spell flash to get out of some sticky situation. If you decided to back unless your really low try to push your minion wave so they die to the enemy turret.
By doing so the enemy laner loose xp. If you stay push the minions then leave mid lane for dragon with your jungler you roam bot or top lane ( top lane is easily gankable bot lane can be harder as thresh or leona or lux can just prevent you from doing what you gotta do.

plz dont waste time attacking the turret at level 6. doing it will most likely end up in you getting not that much early damage on turret and get collapse by the jungler in a bad position( cant shield or you'll get aggro from turret).
in Any case if you do pick a early kill on your laner go roam do something quick you have about 16 second of free time, it can also be farming a jungle camp if there'S nothing else to do.
back. buy homeguard a saphire crystal and kill your laner again. Having home guards early mean that when ever you get a kill on your laner you can roam after cause you can back and come back mid super fast. by level 8 or 10 you can start taking your mid turret but try to do it with your jungler so its safer and quicker. then dragon or a bot lane coordinated gank with your jungler.

In some games, your bot lane ,for some reason will loose there turret super fast and that mean that people are gonna come mid. Be prepare for that and stay behind your turret. marksman have long range so standing about 100 range behind your turret force them to be in turret zone if they ever want to attack you. in a case where you feel your gonna get tower dived pop W.. run back to other turret and wait for back ups. Dont wait under your turret you can probably take the adc really fast with a double ult..but will that put you in a bad situation ? all those question you gotta ask your self ..most of the time the answer is : DIANA GOT A TREMENDOUS LATE GAME,
dont risk anything too much early game and it will pay. so leave turret and back to the one behind no need to die and to loose a turret at the same time. In any case after an event of such sort happens ( or you can be the other team doing it) this means laning phase is over and we get to team fights. An other chapter

I think there people out there playing udyr that would be better to explain to you when to team fight and when to split push . i just wanted to say that Diana can be a good splitpusher as she clear so fast( keep enough mana for the one v one waiting for you at the end of the lane though) Her passive shred towers and lich bane procs are also tower shredders. Most of the time it is better to team fight as you can easily delete any carry in one combo and if you didnt press R too quickly and saved it you can actually chain another kills here and there.
If you Get a good cluster team fight you could easily get penta because or your aoe and R resets and low cooldown Q to chain those kills. (the best final item to help you get a penta in my opinion is riley as it will help in survivability and restrain even more the fleeing help sticking to the enemy even more.
Zhonya's is a most in team fight when you know your getting focused..as you are one hell of a godly initiator.
But taking a good situation where you delete two carry really fast the treat level of the enemy team just dropped a whole lot and a zhonya might be useless/non necessary as it is an extremely expensive item compare to the one's have indicated.

Combo :
-So the Full combo with out 40% cdr is Q R AA W AA E AA Q R . it a long as combo that makes good damage and really pay to weave in the extra auto's as you get your passive up.
-The harass combo is get 2 aa in then QWR AA ( really important to put in the 3rd AA on champ as this combo is expensive mana wise) then walk away protected by your shield.
-The insta death combo Q R W R ( do it fast, with out the E cause its unecessary and cost too much mana)

how to use those combo. At level 6 your gonna use the poke combo to get your enemy 60% heath then 8 seconds later when Q and W are back on your gonna do the insta death combo (i repeat dont use E or you wont have enough mana). This is how you trade with Diana if you can call this a trade.
The enemy to watch out for are Zed that can out play your Q and even R with is ult. Annie ..you wont ever get a solo kill on annie..dont even try it. just pray your jungler is tanky enough to sustain the tiburst and help him after..dont stack pile on each other as she mgith get a double. Fizz is scary for as long as you dont have zhonyah to counter is ult. Malzahar is also scary one v one you need a jungler or a support that as a cc that can stop is ult( having one your self you will be both protected in case he decide to ult one or the other).

Tips
1 : you need to throw Q then str8 after use R ..dont wait for your target to get hit you will still get your R back if your Q land on arrival or slightly after(need to throw Q first always. I guess thats the first thing to pratice on Diana. QR insta combo.the quicker you can do that the quicker they will die.

2: 40% cdr
here's something people might not know with 40% CDR diana Q is on a 3.6 sec cool down..the debuff she apply stay for 3 seconds. Which mean that just before the end of the mark you actually only have a .6 second to wait to re-apply one. You could compare this to Akali's Q but I don't know this is a Diana Guide. not a flippin ninja one.
So Apply the Q wait 2.5 pres R dropping an auto strait after( lich bane proc magic damage, beautiful ) send that Q again R and then R again ..so instead of having only two ults in the proc you get 3 in a really short time frame..doing this will laave you ultless for 9 seconds at level 16 with 40 % cdr

3: Melee fighting and Dragon/Buff taking
This refer to a farming technique that you can also find in my jungle guide Diana Speedclearing.
Q AA AA R AA W AA Q AA AA R AA E AA (loop it )Q AA AA R AA W AA Q AA AA R AA E(this E might be on cooldown) AA Q AA AA R AA W AA Q AA AA R AA E AA Q AA AA R AA W AA Q AA AA R AA E AA

this combo never takes away your ult as you need it to gank/farm/fight. its takes advantage of lich bane on almost every single attack and even got spots where it synergize with your pssive to deal such a burst of damage on an simple AA. The thing is to take the most out of you QR combo by weaving two auto attack in between which can be done in melee fighting. the Q debuff last 3 second which give you the time to do those 2 aa then you press R do the third AA. Boom passive plus new lich bane proc then you continue fighting another AA W AA for another lich bane proc then Q is back on so another lich bane proc and so on. So really liche bane /rune glaive can add a ton of magic damage to your combos just wait 1.5 second between your abilities and you can chain them for really long especially in the jungle or agaisnt a lifey champion like Garen.

4 :Never use R on Baron as it will cc you. just use Q W AApassive

5 if you catch some one out of possition with low healt you can RWEQ them with out them having a single chance of escaping as your Q is the dogeable part hard to miss when sitting on target. This will leave you ultless but not for long and will surely pay off.

the enemy you should watch out for are
-Zed that can out play your Q and even R with is ult. Annie ..you wont ever get a solo kill on
-Annie..dont even try it. just pray your jungler is tanky enough to sustain the tiburst and help him after..dont stack pile on each other as she mgith get a double.
-Fizz is scary for as long as you dont have zhonyah to counter is ult.
-Malzahar is also scary one v one you need a jungler or a support that as a cc that can stop is ult( having one your self you will be both protected in case he decide to ult one or the other).

the enemies you should feast on are
Jinx and any other adc like her that have no mobility as you will delete them so fast they wont know what happened to them.
Any support that is a squishy one, nami soraka sona etc...easy kills right there.
any mid laner that you get the advantage and get out of his turret range is pretty much doomed.
And mostly if any one picks leblanc and you can get a Diana in there..this game is in your favor starts W( your W makes her W deal no damage) and use it only to counter her W then when your level 6 and she tryes to enagge you pop your combo plus ignite . later game her passive will get oblitareted by your shield even if she gets invisible. Its magical to the point that you might first think she got away till you realise her deah is showed in he corner.

Diana is a strong one v one mid laner that can snowball really well and serves as a good initiator. In this guide I showed how to use different combos and to use your runes and masteries to get an early power spike at level 6 and a early game lead with only boots to complete to do such. Remember to take a saphire crystal before the rabadon as you will need the extra mana to get your first solo kill easily by doing the harass combo into a insta death combo. In conclusion i'd like to say that Diana is a fine champion with a high skilled cap mechanics, and it takes patience to actually pulls the combo with the most lich bane procs as you need to wait 1.5 second between your abilities. The difference between good and bad diana plays will be made on R resets decisions and summoner spells uses. Now that said you got the potential to do a Penta Go get hem :D.