This is where i'll post all the updates to the guide and Ahri, and let you know of any changed that will happen to her, any items that she use or will use/not use in the future.

-Guide has been Created on 12/18/2011 1:03 AM GMT +2.

THE GUIDE IS UNDER VISUAL MAINTENANCE (Hopefuly by tomorrow i'll get it complete).

PS: This is my very first guide I've ever made so be soft with the comments <3.

Ahri is the brand new champion riot games have created for league of legends, They've been working on her for a long time and the hype was BIG. On Day 1, I realised it was worth the wait.
I'm a big fan of korean/japanese/chinese culture and the nine tailed fox is one of my favorite legend stories That i've studied about.
That's why I figured I should make a guide for her for people who may not be as experienced with this type of champions but are willing to learn and improve with time. I'm not the best Ahri player nor ever played ranked with her before but I made this guide because I want to improve others and improving my own skills aswell during this guide.

I will keep this guide updated and let you know of any changed that will happen to her, any items that she use or will use/not use in the future and anything else that comes so... Stay tuned :).

Ahri is a mage caster assasin which exceels at toying with her foes before delivering the finishing blow,she has great mobility and a brand new cc to encounter.She requires alot of skill to master her but if you'll play her alot you'll get the hang of her skills and find her dominating your enemies with ease.

Pros

-Ahri has great mobility with her ultimate and can chase in for the kill or escape with ease.
-Ahri deals true damage with her Q ability allowing her to ignore any magic resist.
-Ahri prioritise enemy champs over creeps with her skills.
-Ahri has a new type of cc and people are still learning how to counter it.

Cons (and ways to counter them)

-Ahri's Charm spell can hit minions which makes it very hard to land unless you sacrifice one of your ultimate charges or a flash, deals low damage and has high cooldown. Don't get me wrong, it's extremely vital to use it in most cases but just pointing out.

-Ahri has low base mana regen without runes for it or blue buff, forcing some players to get mana regen runes.
can be countered with sacrificing your build a bit by buying 2 doran rings.

-Ahri is quite easy to take down if her ultimate is on cooldown, a skilled player will juke the enemy to escape but in most cases she will go down fairly quick.
-Ahri's Skills are skill shots and auto-target skills, leaving her with with no target skill and requires alot of skill from the player, therefor, It's a tough champion to master.

To counter that : Use smart cast by going to your keyboard bindings and setting it so you can just place your mouse on the direction you want to fire an orb of destruction for example and it will automaticly fire to that direction, without pressing Q and clicking on the direction you want which takes time and might go wrong. Parcice for perfection :).
About the auto target skills, if it's a champ, it will automaticly target him instead of a minion, so use your skills wisely.

-Ahri's base mobility is quite low compared to other casters while she starts off with 305 movement speed and other casters start with 5 more making her a bit slow, easier to be catched while her Ultimate is on Cooldown.

You 4 points on the speed boost from the utility tree sure helps a bunch and if you think thats not enough for you, you may buy a speed qunit rune.

Ahri can go with a few types of runes. I'll go over the ones I have and I'm using for her but i'll point out some good ones others may find better or suitable for their own way of player her.

My Set :

-For marks I take Greater Mark of Insight for magic pen, no more detail.
-For Seals I take Greater Seal of Force for ability power per lvl, since her ratios with ap scale quite low, the flat ones won't be that good for early game, so I work on her late game.
-For Glyphs I take Greater Glyph of Celerity for flat ability power but I'm going to change it to Force for ability power per lvl for the reason I mentioned.
-For Quintessence I take flat ability power, that gives me a nice early game damage and I find it better than ability power per level in this case.

Suggestions :

-Other marks that might suit her would be Greater Mark of Force for more ability power per lvl, I won't prefer it over Insight but up to you.
-Other seals that might suit her can be Greater Seal of Replenishment, since you need mana regen for early game or if your team won't give you blue.
-Other Glyphs I would suggest can be Greater Glyph of Focus for cd reduction or flat ability power since they get most ap compared to marks or seals.
-Other Quintessence you can try are Greater Quintessence of Insight for magic pen,Greater Quintessence of Vampirism for more spellvamp to scale well with your passive or Greater Quintessence of Swiftness to cover your movement speed issue.

For masteries I take 21/0/9 for Summoner's Rift and 22/0/8 for dominion and twisted treeline.
On offense I focus on ability power, ability power per lvl, magic pen, increased damage, ability power %, and Executioner which is the bread and butter 6% more damage for champs below 40% health to finish them off. On utility tree I focus on Mana Per Lvl, and increased Movement speed.. Depends on the map you're playing, you may take 1 point for more ability power on offense or 1 point for Runic Affinity for increased buff duration for actually all maps but I find it for dominion and twisted treeline a bit less useful, But it's based on personal prefrences.

Flash - In my opinion is perfect for ahri, Can save you from many threats or make you a threat to someone else. It's her only safe escape way when her ultimate is on cooldown. Very good spell, enough said.

Ignite - Take out enemies or injure them, or reduce their healing procs. Very useful on healers such as warwick,tryn,mundo and more... Increases your burst and basicly set as your finisher if you all your skills are on cd. With the mastery Summoner's Wrath you also get 5 ap and ad while it's on cooldown.

Ghost - I usually use this for dominion to capture points quickly or escape enemies. I would like to mention that I do give up on flash at dominion since it's not very useful in there.

Exhuast - Could be a good spell for saving yourself from getting pwn'd hard by a melee ad, chase targets without Ryali's proc (if you don't have it yet or not use it for your build), and if you have a point in Summoner's Wrath on offense tree you get a benefit of 10 magic resist and armor reduction on your target. Useful.

Teleport - Good for setting up ganks or babysit. Not so useful for her in my opinion unless it's a premade strategy.

Clarity - The mana you get from it is truly great for early game but when it gets to mid game and you start getting blue or even have 2 doran rings / or have mana regen runes, This spell becomes useless. No thanks.

Clairvoyance - This spell is something to discuss about. Not many supports take this often for the reason of : "I have a getaway spell such as flash and I need mana so I take clarity". People may have not noticed but Ahri could be a decent support. Her charm spell is a really good initiating skill and shes very mobile with her ult so during a teamfight she could debuff the entire enemy team and let your buddies finish them off. I will discuss about a build for this, defenitly. If you will go support take this, Please. Can prevent you or your teamates from getting ganked and checking on dragon and baron every once in a while can be crucial.

Cleanse - No, Quicksilver sash if you're getting cc'ed heavily.

Heal - Can be somewhat useful if you're laning and in teamfights.. But not for the main ap build.

Spell Combos :

Flash&Ignite - In and out, finisher/reducing heals.
Ignite&Exhuast - Amazing burst damage with it, an instantkill 80% of the times.
Ghost&Flash - No one can catch you or get away from you.
Ghost&Ignite - Capture those points and finish them off in dominion.
Teleport&Clairvoyance - Babysit other lanes and keep track of buffs/dragon or incoming ganks.
Clairvoyance&Heal - Keep track of buff/dragon or incoming ganks and heal your team during a teamfight.
Clairvoyance&Flash - Keep track of buff/dragon or incoming ganks and get out or in the fight.
Heal&Clarity - Can't trust mana regen or your team for blue buff? Clarity got your back, all out on support with these two.

* The reason I'm not mentioning surge is because it's somewhat useful, at level 1 you get 10 ap boost and at lvl 18 you get 78 ap but the cooldown is rather long and the other benefit doesn't really suit ahri (attack speed%).

The reason behind my skill sequence you might have been asking yourself, why am I maxing orb of desception first or why maxing firefox first before charm and why make it abit complex.
So, Orb of desception is Ahri's main creeps cleaner, it deals quite a bit of damage to what comes in its path therefor extremely important to level FIRST, So I'm done leveling it by level 9. Ultimate is at 6,11 and 16 as usual. About firefox/charm order. I pick charm second for some good initiating if anyone on my team wants to gank, or to save myself from being ganked. Now the reason I'm maxing it last is becaue it's very hard to land on someone when there are waves of minions around you, And in early game, farming means minions are around you so.. No good. It is very useful, but firefox gives more burst damage and makes it far easier to get passive stacks with the combination of firefox and orb of desception. When firefox is level 3 I put a point on Charm to balance it, basicly for more damage and duration/effect on the target and because it turns to mid-late game by than.
If you don't like this order you may level charm before firefox for more duration/effect but you'll lose some burst damage so In my opinion = Not worth it.

Doran's Ring(s) - Very nice starting item, you're squishy so the extra health always helps.. more ability power and the mana regen that you most certainly will need if you don't have mana regen runes and just go for ability power kind of seals. Why 2? Makes you more substained with the extra health and regen, of course the ability power aswell. I'd say it's worth the money because they stay with you untill mid-late game.

Sorcerer's Shoes - Speed and magic pen. Basic caster shoes, enough been said.

Morello's Evil Tome - This covers many aspects for Ahri. Mana regen, Cd reduction AND more ability power. Great item, a must for Ahri.

Rylai's Crystal Scepter - Gives you health, ability power and it's main ability which is reducing 35% movement speed for spell damage done, and if it's an Area of Effect (AOE) skill it gets 50% movement speed reduction. If you hit a minion and your target gets hit, it reduces his speed by 50%, extremely useful with Ahri.. More substained with the HP and the passive is truly great. Can slow chasers or slow runners. Love it.

Rabadon's Deathcap - Caster item must for all casters out there. period.

Will of the Ancient - Very good item for Ahri,Procs very well with her passive and make her way more substained as she can clear off a mob of minions or a jungle and get back in a fight like she never lost hp.

These are the items that I use for every game and usually it works pretty well.
For the last item I have a few that can work pretty good in some situations.

Abyssal Scepter - If no one on your team has it, pick it up and enjoy the ability power, magic resist and the 20 magic resist reduction aura to surrounding enemies. Quite useful lategame if no one at your team has it and your foes are resisted to magic (tanky) AND if you have another ap based champ on your side.

Deathfire Grasp - It's active can destroy anything in 1 shot. I take this if I have squishy foes to destroy them in an instance. Very useful.

Void Staff - Ignore their magic resist almost completely. big damage boost.

Lich Bane - An insane damage boost, after using a skill you trigger it's proc and you auto attack it deals physical damage as your ability power, which at this point can be over 700. Gives also extra 7% movement speed and 350 mana.

Other than that, any kind of defensive item to counter your foes and stay alive in teamfights, I wouldn't suggest thornmail though since you won't last long enough to make him enough damage to himself to kill him like rammus does, but any kind of magic resist item such as Banshee's,Quicksilver Sash,Force of Nature can be decent. Her armor isn't very high but wouldn't matter much if she had some more.

These last items are really up to you. Take abyssal if you just want to help yourself and teamates deal more magic damage passively, Deathfire grasp if you're well with using your items, Void staff if your enemies has lots of magic resist or Lich Bane if you use auto attacks at your combos, or any magic resist item with a good passive/active or just force of nature to counter their ability power carry's.

The Sequence for the items :

Start off with a Doran's Ring > Farm till you get about 1K gold > Boots of Speed and Doran's Ring > Farm either 1.2K Gold for Giant's Belt or 1.95K for both Giant's Belt & Sorcerer's Shoes > Get 1.72K gold for 2 Blasting wands, 1 for Rayli's and 1 for Morello's and get Morello's Evil Tome and Rayli's Crystal Scepter one at a time, order doesn't matter much > Farm 1.6K for Needlessly Large Rod > Rabadon's Deathcap > Hextech Revolver > Will of the Ancients > Last item.

This is how I usually build Ahri in this specific order.
There is one item that people grab as their first item which I think is unneccery which is the Rod of Ages. Gives her some decent health/mana/ability power every minute is mainly there for the passive that gives you extra health/mana per level. This can save your butt many times during a fight and make you more substain in lane but I find it delaying the actual build and the damage output of Ahri won't do much untill its maxed out. And by level 18 they sell it and get a Rayli's.. So I rather play straight forward with the usual build for her that I think is best for her.