~FOX~
I've never actually made a guide before, so bear with me. I'm not a pro, nor close to it, so keep that in mind before blindly rushing my guide. It's fairly consistent with most Ahri builds however so I think that won't be much of a problem.

This is a guide to Mid AP Ahri, though sometimes you'll see her top or bot (usually from switching). I have tried AD Ahri before and I have to say it's actually rather fun, but I've not played it enough to comment on it.

One last note, you must ingrain GG's Run Devil Run song into your head before playing Ahri. You'll never get far without it.
Play Video
You better run, run, run, run~

Start

Midgame/Core

One of:

Mid/Lategame full builds

Possibly:

These are pretty straightforward.

MARKS
Greater Mark of Magic Penetration: The only reason I see for not running these is for going as an AD Ahri, in which flat AD or ArPen would be better. They increase your damage output more than any other mark as AP Ahri.

SEALS
Greater Seal of Armor: I tend to run these by habit since I harass with autos as well as spells. They reduce minion damage, monster damage and retaliating autos.

Greater Seal of Vitality: This is similar to running armor, but it's scaling HP instead. Don't run the flats, you won't need them and they break even much earlier than you'll ever need the early HP boost for.

Greater Seal of Scaling Mana Regeneration: You may decide to run mana regen instead if you aren't taking as much physical damage or harass more with spells. Personally I feel like these aren't quite necessary but other people may find them useful. It's flat regen counterpart is okay as well, but falls off fairly fast.



GLYPHS
Greater Glyph of Scaling Ability Power: Scales you much better into lategame. The flat counterpart isn't quite as necessary as you aren't an early game burster.

Greater Glyph of Magic Resist You might want this or its counterpart if you're in a hard matchup against an AP or just feel weaker overall. I don't use this as much due to incorporating negatron cloak in my build later.

If you opt for the mana regen glyphs, just make sure you don't go all in all the time. It'll make you fairly squishy and weaker later, but I know several people like it better.

QUINTESSENCES
Greater Quintessence of Ability Power: Honestly the best choice in my opinion, you get free early game AP and the other choices aren't quite as useful.

Greater Quintessence of Movement Speed: If you feel like you need to kite harder/get kited a lot (which shouldn't happen often) you might consider MS over AP. I don't think it's as useful, especially since with the movement speed masteries and tier 1 boots Ahri is already able to gank side lanes in between waves.

These are personal/majority opinion, but feel free to use other runes. I'm not the one playing your Ahri.

I'll keep this short, since variations from the one put up above won't change much.

I take all the AP and related masteries in the offensive tree. This should be fairly obvious. If you're going AD, you'll want the attack damage ones (obvious).
Make sure you don't accidentally put 4 into the first AP mastery, it's a bit useless having an extra point of AP in exchange for improved ignite/whatever.

One note: I do take the initial +3 AD over +3 AP because +3 AP doesn't do anything but the AD helps with last hitting and harassing.

I don't run anything in defense usually. If you feel like it's a hard lane, go for 9 in defense. Put in armor/MR accordingly and just go for the +30 health route. It's pretty straightforward.

I'll usually get 9 in utility. I get the mana for... mana and improved flash for obvious reasons. Most times I opt for more MS, but you may want mana regen if you find yourself OOM fairly often. Get the improved buff mastery so you can keep your blue and red buffs longer. I love red buff.
(and blue)

Ahri's got a few choices, but the two most common:
Flash: HUGE for making plays. You get to blink over things, make aggressive plays, leave, kill things, whatever!
Ignite: Kill more things! This also reduces healing by 50% which is pretty big against some champions (Vladimir/Swain I'm looking at you two).

If you don't have either yet (smurfing, I'd bet) or just don't like them (boycotting flash, sux2suk), you can get these options instead:

Ghost: Since you already have three flashes, you might opt for Ghost instead. However, it's not instant distance and with three flashes you won't really need to gap close with it. However, it's decent on bruisers and tanks because they're tanky enough that they can cover more distance overall with ghost.

Exhaust: Offensive AND defensive. It's slightly weaker on AP champions but can net you kills, especially with a jungler. You'll live more often with it however, especially when being tower dived.

Cleanse: Um, maybe you're just dying a lot and getting hit by CC. It's not really that useful on Ahri especially as you already have 3, possibly 4 flashes, but it has it's moments.

Surge: Extra burst? This is kind of pointless, but since it gives AP it could possible work with Ahri. It's not recommended however.

Anything else is kind of pointless. To be fair, Surge and Cleanse are also kind of pointless.

: It used to be called Soul Eater, which was Nasus' passive. =(
Anyways, this accounts for Ahri's lane sustain. It doesn't seem like too much at first, but it's pretty noticeable. Some people get spellvamp for this reason, and it's not a bad choice.

: Ahri's main source of damage. It's similar to Sivir's Q, but comes back with true damage. Hitting it at max range will instantly chunk them for both parts. It's a pretty good farming tool along with W and with about 40~ish AP and at level 3 should be able to oneshot caster minions.

: This lets Ahri trade with so many champs in lane. It can knock off Morde and Morg's shield as well as get off free damage. Each fire is single target, so you get the full Rylai's slow with them. They're also 800 range each and prioritize champions.
Max this second for damage and trading. Very rarely will you want Charm maxed second, and I've never been in that situation.
You may also max this first instead of Q. It does equal base damage but scales better by .14 AP (if all of it hits). Consider this against melee mids who can get hit by all 3 fires consistently, or against weak pushers. For obvious reasons you shouldn't do this against champs like Mordekaiser or Morgana or TF.
Just remember, if teamfights begin, a max W won't help quite nearly as much as Q in terms of AoE damage (3 single target bursts that might not even hit the same champion). It's still a decently strong alternative to maxing Q however, especially in duels.

: OP TAUNT IS OP. Fairly long range, decent speed and one of the most ridiculous CCs in the game. It's like a Blitzcrank grab, but... not really. If you haven't played or played against Ahri, it's basically a ranged taunt.
The most obvious use is catching people out of position and level 1 invades. You should also use this when escaping, as it slows them (and they're coming to you, anyways).
Good players should be able to land this 90% of the time. I've yet to reach that but it's gamebreaking.
This is maxed last, as you won't need the lengthened CC as much as damage. Charm is mainly used to catch people out and lead them into more CC, so the extra second won't be as needed.

: Ahri's three flash ultimate. Aside from adding damage, you can use it for escaping in lieu of flash as well as setting up ganks with your Charm. It goes through most walls as well, similar to flash. You won't be able to ult over the thickest parts of tree in the jungle, but most areas will be fine.
I may get a map for this if people need it.

YOU SHOULD NEVER FOLLOW A GUIDE'S ITEMS STRAIGHT UP WITHOUT QUESTION.

That being said, if you're trying out a build you should still keep the core of it at the very least. Just because they have a lot of MR doesn't mean you should go straight up AD Ahri (but you never know...)

STARTING OUT

AP or AD, Boots + 3 Health Potion are your best choice. They're the safest for invading, laning, whatever. They'll also give you enough sustain to get your next big items.
Taking a fourth pot or a blue pot is just as viable. It will make you miss some early cs, but might pay off later.

Doran's Ring is another choice. I find this a pretty rare option, as it's very risky and won't give you as much sustain or mobility. If you can manage to trade well (melee mid perhaps with weak harass) you can run these. They'll give you a strong early game, but you're especially susceptible to ganks.
Furthermore, boots will give you the MS to dodge skillshots with ease. Doran's will give you the HP to tank it but not the MS to dodge it altogether.

Those are the only two beginning items I will ever use on AP Ahri. Some of you may like Amplifying Tome + Health Potion, and that's okay. I personally will never use that as it's fairly weak in my opinion. You get +5 AP more than a Ring, but without the survivability or mana regen. You get 2 pots less than a boots start in terms of sustain.
Her passive may get you a tiny bit more health back than if you ran ring or boots, but overall you're losing out on either mobility and sustain, or survivability and regen.
Finally, it's a fairly useless item until you upgrade it into Rylai's or Revolver, which you might not always want.

BOOTS?

You have 4 options worth picking (and, well, if you really want to do AD Ahri, you can get Berserker's Greaves)


The most common option. This increases your damage output, and is pretty straightforward.


This gives you CDR, which will make you a little more spammy. I don't find that it increases damage much, so I rarely use it.


MR? Tenacity? NUMERO UNO if you need survivability. This is a decent lategame option when Sorc's become less relevant. You will likely die anyways however if you get hit with CC though so I don't use it quite as much as I do Sorc shoes.


Honestly only when they have a 4 AD team comp and I need survivability against gap closing offtanks/tanks. This is kind of a weird pick and most people won't go for it.

MID GAME/CORE

Depending on how you're doing, you may need a third Ring or only one. I take two for the early game stats (survivability, regen, damage, etc).

Now, you may not be building Blasting Wand, but all of your initial big purchases require one. Depending on your matchup and how you do, these are the items you will want after your double doran's:


If you're doing well, get a cap. They look really nice on fox girls. More importantly, it'll make your ganks deadly and laning much easier. You spellvamp more, your damage is better, and you'll be able to get kills much more often. It's a little risky, but it pays off in spades. Never get this if you're in a bad matchup or losing, it won't help.


This is the anti-AP route. You'll want this against early game mages or if you're against a double AP team comp. You should always be getting Negatron Cloak first. It's kind of the point of going this route. I personally use it against LeBlanc, Annie, Brand and sometimes Cassioepeia.


This is the safest route and fairly strong whether you're dominating or not. It gives survivability and AP as well as a slow on all spells, which makes escaping and ganking easier. I get this in almost all of my games.
Take Giant's Belt first if you opt for this path unless you feel like it's a very passive lane. It's much more forgiving. You may want to get one after your Needlessly Large Rod for a strong midgame, and then build up into either Rabadon's Deathcap or Rylai's Crystal Scepter


Getting a Revolver early will definitely help laning phase. You can stay in lane forever. If you do like this route, take mana regen as you'll need to cast spells to actually utilize the spellvamp.
WotA is for similar reasons as good choice as it'll increase your sustain and give you decent burst. Due to its recent nerfs you shouldn't rush it though.
WotA is very useful when running double or even triple AP comps. It only stacks twice though.


I very rarely go this route, but it's viable and not as rare as you'd think. Though Ahri isn't exactly an instagib champion, it gives her a strong single target burst and decent AP. Take Kage's Lucky Pick if you're going for this item.
You must use the active or it's useless. Always activate it first, before anything else (except Charm to get them in range). This is because it's damage is based on % current HP, not total HP.

You will likely want Rabadon's Deathcap and another item, like Rylai's or Abyssal. Occasionally you will find yourself getting a third, like WotA.

LATEGAME

You have a variety of choices, but you should be building based on the game.


The most obvious choice. It's very cheap and boosts your damage a lot due to people picking up MR. Never get this early: it's %-based magic penetration.


It gives you decent burst, armor for those AD carries and offtanks who'll be jumping on you and an active that will probably save your life. Despite this, it's not as effective as it is on champions with channeled ultimates like Morgana or Fiddles.


This gives you a Cleanse active on a short cooldown (60 seconds). If you're getting caught (please don't) or they have a lot of CC, take this to survive and continue to be relevant.
All I have to say is, remember you have this in your inventory. It's kind of useless except as an extra bit of armor.


Fairly unorthodox and I've never used it, but some people find the HP and regen useful. I personally think it's kind of pointless and just elongates your death if you do get caught, but I'm just being pessimistic. If you have QSS, you might want to maximize your EHP with Warmog's.

NOOBTRAPS

By the time this becomes relevant, you'll be dead from autos anyways. You don't have the HP to support it's passive, so when you get hit by autos you'll be getting chunked for 300-400 HP at a time, if not more.


Pointless unless you want max AP build. She isn't that mana hungry and she's pretty squishy so this is just extra mana and AP.

I'll probably update this section as time goes on.

Level 1 is where THE BIG PLAYS HAPPEN ...sometimes.

You should never start with an ability right when you begin the game, unless there is literally no other choice (none of which I can think of right now, but Alistar will probably use Q over W first anyways).

With Ahri, you'll only use Q or E in invades, so get ready to pick one or the other first. For example, if Blitz grabs someone, you'll want E to keep them within the team. However, if Alistar just flash Q'd half their team, you'll want Q to maximize damage. Despite this, it's a safe bet to go with Q.

When you reach your lane, you don't want to Q at all, unless maybe for getting two creeps who are both low. This is because it's damage is minimal and you're using up mana that will become more relevant as laning phase goes on.

Once your Q is level 2-3 you should begin to harass with it. The easiest is when they go in for a last hit, particularly one close to you. Just fling your Q in their direction and they'll have to take both hits. W is also a fairly strong tool, especially when trading. They'll most likely take 2-3 fox-fires as well as both sides of your Q.

When you harass, measure it out so that you don't force a recall too early (before 6). 50% HP is usually enough. When you're almost 6, you can push the lane to get it before they do. Ctrl + R to autolevel your ultimate and jump on them with R>E>Q>W ignite. Be careful of champions who have shields (except Morgana and Morde pre 6) or stuns, as that will turn the tables on you.

Be aware of their cooldowns, your mana and theirs, their spells, and your damage. Misjudging them can lead to no mana for Q, getting hit by a stun, or just not killing them. You may have to dive tower - make sure you can flash out. NEVER flash in under tower for the kill unless you are confident you can make it out alive. That applies to virtually everyone at this point in the game.

Also, remember to buy your Sight Ward constantly. Usually one or two every time you back if you have the gold for it, as well as possible pots if you need them.

Your first back should be when you have 1200-1500g. This lets you get two and wards/pots if you need them, or a revolver if that's your thing.
If you got ganked and had to back early, make sure you get a ward or ask your jungler to do so. Ahri is a fairly high priority pre-6 ganker due to her mobility post-6 so they will want to kill you before then.

By midgame you should have your or related items. You may have a instead of / .

Whatever it is you have, fights should begin breaking out. Wards are your best friend here: you will be able to catch people with your charm who don't know you're there. When you fight, keep away and Q/W/E from a distance. Ulti only to catch people or when you're winning, and try to leave a charge open in case you need to escape.

When you're stealing Dragon, make sure your jungler is in position. Ulti in and Charm their jungler so he can't Smite, giving your (hopefully proficient) jungler the chance to Smite it.
Alternatively, you can E the closest person and initiate on them.

You will never have a set rotation during fights, but generally opening up with E is very standard.

This is when you really need to Charm consistently. Charm makes THE BIG PLAYS!

Charming over walls isn't very effective unless your team can follow up. This is because it just taunts them; however if you can catch someone in the jungle with R>E, do it and turn the fight into a 4v5.

People will begin contesting Baron; it's the same idea as with Dragon, but you can't ulti over and Charm without risking severe consequences. If their AP is guarding it, Charm them; otherwise if it's a very strong tank, there's no point and you'll bait your team into focusing him. Save it for a clearer shot at a squishier target, or to peel instead. If their tank is weak, you should Charm however; it's a decision you have to make. Tanks are fairly important for initiates and peeling.

Make sure your team is warding Baron and pushing without overextending, and if you see the opportunity, R>E a laggard or lone wolf. As an assassin, you should be trying to catch people with your team and killing them, putting them at a severe disadvantage. Inhibitors are incredibly important at this point; they increase your map advantage so much.

DO NOT EVER JUMP IN WITH ULTI.

By lategame, everyone is fed. That 0 11 Vayne is finally becoming a threat. Their 1 6 Cassiopeia is now relevant. Anyone and everyone will kill you. Do not use your ultimate to supplement damage until it's cleanup phase, when the team is low, or you're catching someone with R>E and the majority of their team is weak or dead.
By this time, their AD can and will kill you and tanks will peel for them. Stay back, Q/W and E their offtanks, but do NOT ulti until you're sure you can survive.

I'll definitely add more as time comes, I did this all early in the morning and there's probably a lot of off/awkward information in it. I might put in a few matchups as well, or maybe some images. Everyone likes pictures.

As this is my first guide, I haven't quite got the hang of it. Leave comments or w/e you want, I'll (probably) read them and respond.

Uh... yeah

run devil devil run run