Ahri is a great champion to play. She has a cc, many aoes, and she deal a massive amount of damage. This is the way i build her, please feel free to criticize. It only improves my guide. Have fun and good luck~ Make sure to read all the tabs or this build might be a little confusing.

March 8. 2012 - Created this build :D
Marck 12. 2012 - Edit Items, Added to the 'Situational Items' tab and 'Follow this build and .....' tab. AND added in a 'Finished Item Build' Tab.
March 14. 2012 - Redid Summary tab and added more pictures of my scores :]

Ask a question in the comments below and ill make sure to answer most of them in this tab. :D

PROS.

HAVE YOU SEEN HER DANCE? IT'S RUN DEVIL RUN BY SNSD. GO KOREANS. :]
True damage
CC.
A lot of Aoes.
Built in Spell Vamp.
Built in Escape from ganks and deal damage, and Chase and deal damage ulti :D

CONS

Hard to aim skill shots.
VERY squishy
Easy to die before level 6

Mercy is a human luxury... and responsibility.
-Ahri

Unlike other foxes that roamed the woods of southern Ionia, Ahri had always felt a strange sonnection to the magical world around her; a connection that was somehow incomplete. Deep inside, she felt the sin she had been born into was and ill fit for her and dreamt of one day becoming human. Her goal seemed forever out of reach, until she happened upon the wake of a human battle. It was a grisly scene, the land obscured b uthe forms og wounded and dyin soldiers. She felt drawn to one: a robed man encircled by a waning field of magic whose life was quickly slipping away. She approached him and something deep inside of her triggered, reaching out to the man in a way she souldn't understand.His life essence poured into her, carried on invisible strands of magic. The sensation was intoxicating and overwhelming. As her reverie faded, she was delighted to discover that she had changed. Her sleek white fur had receded and her body was long and lithe - the shape of the humands who lay scattered about her.

However, though she appeared human, she knew that in truth the transformation was incomplete. A cunning creature. she adapted herself to the customs of human society and used her profound gift of beauty to attract unsuspecting men. She could consume their life to essences wher they were under the spell of her seductive charms. Feeding on their desires brought her closer to her dream, but as she took more lives, a strange sense of regret began to well within her. She has reservations about actions which never troubled her as a fox. She realized that she could not overcome the panfs of her evolving mortality. In search of a solution, Ahri foung the Institute of War, home of the most gifted mages on Runterra. They offered her a chance to attain her humanity without further harm through service in the League of Legends.

Amumu: Stuns and ulti all 5 people. (Tank)
GangPlank: Ulti can deal damage when amumu ultis. (AD)
Nunu:Ulti with Amumu :D (AP)
Ahri: Ulti in and kill everybody. (AP)
Ashe: Slow everyone and stun SOMEONE with Ulti (AD CARRY)

For some magic penetration, I got Greater Mark of Magic Penetration and Greater Quintessence of Magic Penetration. I got this because incase the enemy team stacks up on mr, it'll be hard to deal damage. Magic penetration runes can help that and you can deal more damage. Getting more ap isn't the best idea. After that, I got Greater Seal of Replenishment because in early game, Ahri can tend to be a little man hungry. It'll be hard to try to kill your opponent. If you have slained Ancient Golem you get a buff. Even if you have this buff, it'll eventually go away. This rune helps a lot on regening mana when you dont have the buff. The Greater Glyph of Scaling Ability Power is great because it give ap every level which eventually adds up to 28 ability power at level 18. More Magic Damage :]

This is skill sequence from 1~18. I suggest you max Orb of Deception first because this is your main damage dealing spell out of the 3 spells (not including ulti). Get Fox-Fire next because Charm is good enough with one skill point. Although Charm may stay on a little longer if it is maxed, Fox-Fire will deal a lot of damage with one combo.

1/1 on Summoner's Wrath. 4/4 on Mental Force. 4/4 on Sorcery. 1/1 on Arcane Knowledge. 2/3 on Havoc. 4/4 on Blast. 4/4 on Archmage. 1/1 on Executioner. 1/1 on Summoner's Insight. 3/3 on Expanded Mind. 1/4 on Swiftness. 1/1 on Runic Affinity. Havoc does give damage, but it's the only good thing i can put on to move on to blast. Everything else mainly concentrated on magic, mana, and cooldowns.

As you can see, i did get Catalyst the Protector pretty early because Ahri runs out of mana really fast especially if you play really aggresive like me. After I got Rod of Ages because the UNIQUE -which means it doesn't stack- Passive give 18 mana, 20 health, and 2 ability power every minute and recovers mana and hp every level. So this is an AMAZING ITEM ON AHRI especially if you farm enough to get it early in the game. Sorcerer's Shoes give some magic pen and that's great if the opposing team build lots of mr. I never thought of getting a Morello's Evil Tome because i never thought it was good. I don't like Ionian Boots of Lucidity on Ahri and Morello's Evil Tome give ap AND Cd reduction. I thought that was really good so i got that because my skills took FOREVER to load. Finally, An Rabadon's Deathcap is really good on Ahri because it makes you deal MORE damage. Wanna know why? It's because the UNIQUE aura is it lower's enemy team's magic resistance AND gives ap AND gives MR. 3 things in 1 :] And this item isn't as expensive as other items.

Dieing too fast? Consider getting a Guardian Angel or a defensive item depending on opposing team's balance.

Too weak? Consider getting a Void Staff

Want more ap AND defense? Consider getting a Rylai's Crystal Scepter or a Abyssal Mask

Wanna know my suggestions on the last two items? I'd get a Abyssal Mask and a Void Staff or a Guardian Angel and a Void Staff OR a Will of the Ancients and a Void Staff. It depends on how fast you die and how fed you are :]

So, the recommended finished item build is:

This is not the most effective in some games. Do not get these exact items. Try to add in some other items. Look in the Situational Items Tab and figure out what's best for you and your team.

Run away AND chase. Also, this would work really well if you ulti, all three times, but you regret it. Just flash out and you'll be fine, unless the opposing team slows, silence, stuns, or snares you. :]

It does often kill someone for you when the enemy you were fight is lit (low hp) and ran away. When their lit and u know they'll do something about running away, press f or d and click on them and after a few seconds, you'll see that you got a kill. :]

Other good options for ahri...

This goes great with Spirit Rush, but it's not so great with running away because you might get stunned and use ghost to run away, but waste it. But if you feel more comfortable with Ghost it's fine to use it.

use this to get a free kill of of someone. It's rather op. Exhasut slows, reduces 70% of their attack damage, and and reduced item and ability damage deal by 35%. Thats a lot in one skill. You can Exhaust and taunt. They'll be harmless and they'll be screaming when you use one combo and kill them in 2 seconds. :]

Teleport is also great if it's difficult for you to hold a lane with Ahri. So if you are having problems with holding a lane in your previous game with ahri, use teleport.

The items for this build was :
:]

So, how'd you like it??? :] I worked really hard on this buils and please give me advice on what i should or shouldn't fix. Check out my other buids too and have a GREAT time with ahri. I'll try to add more to this build once i figure out mobafire even more. I'm not exactly pro with building guides, but i tried so yeah.

Have fun~
Good Luck~
Give advice~
Thank you for reading :]