First of all let me introduce myself: Im a 23 year old dude from germany,
playing LOL since the beginning of 2012.
I prefer AP mid-lane or AD-Carry, but can do all the roles a little bit.
My 'main-champs' are Morgana/Ahri (mid) and Ezrael/Ashe (bot).
Sorry for my bad english (i left the shool 7 years ago),
but hopefully you will get most of the facts about my style of play.

I think its nessecary for Ahri to be Mid-lane, because she needs the full farm!
Maybe she can do solo-top, if someone tanky like mordekaiser wants to do the mid-lane.


So lets start with the guide: I will tell you why i like Ahri so much and think that she is a beast.

She is a versatile, mass damage dealing champ with a nice ulti to escape.
Her sharm is probably one of the best CC's in the hole game.
If you land the flying heart, the enemy walks harmless in your direction.
She got a very nice passive, if your spells do damage to 9 minions/monsters/champs your next ability
has got 35% Spellvamp. Thats a lot!
The only problem is her squishiness, like most of the mages (especially damagedealer).
But if you are doing good in positining and use the ultimate wise you simply can not die.

Pros
.
+ very powerful if farmed well
+ Nice CC (sharm)
+ does true damage (Q-Spell if it comes back)
+ best escape ult in the hole game
+ your orb (Q-Spell) can do damage on the hole enemy-team
+ good minion-pusher

Cons
.
- Squishy
- Q & E are skillshot
- Spell-dependent
- mostly dead if stuned
- probably not the easiest champ to master

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Ok, the best runes in my opinion are:
- Quintessenz: 3x 5 AP Runen <- for the extra damage early game
- Marks: 9x Magic Penetration <- for the extra damage early game
- Glyphs: 9x Magic Resist <- most of the times mid is for AP-champs, so they dont do so much damage
9x AP per lvl <- 27(!) extra ap at level 18
- Seal: 9x Armor per lvl <- it is good in teamfights mid-game
9x Mana Reg per 5 <- i like to harrass my opponent, so its a good extra (before i get the blue)

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My Masteries are 21/0/9
The 21 Points in offense ist the most important, because you want to do tons of damage^^
I do the leftover 9 Points in Utility, because of the mana-reg. and i want to make the buff-duration longer.

Another good way is to do the last 9 Points in the defense, if you need the extra health and Magic-Resist.

You can go 9/0/21 too (for cooldown reduction), but i think it is not worth it. You choose!

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Summoner Spells:
1. Ignite or teleport

Ignite!: For the extra damage. This can make the difference 1vs1 (What should i say more?).

teleport: I played ahri a lot and i think teleport is also a good alternative.
If your team already got 2-3 ignites (to counter Mundo, Trynda ...), you probably can take this spell aswell.
If you go back to base -> buying, you can teleport directly to a ward on bot or top and gank the lane, before
they even notice you. (Ahri is a good ganker, because of her sharm.)

2. Flash or ghost

Flash!: This Spell will rescue your life. I cant count how much time this Spell saves my ***.^^
You are right if you think we got the 3 Flashes of our ult.
But we will get it first at level 6. You know that are probably 2 ganks mid.

Ghost: Good alternative because of the lower CD. You can argue again that we got our 3 flashes-ult,
but because of the CD on the ult, i think flash is better. But its a personal preference.

If you are crazy you can take Ignite and Teleport as well. So your escape-spell is your ult.

Other viable choices are:

Heal (probably the extra health to kill your enemy or to run away)
Exhaust (can be used as an escape or chase spell)

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Item-build:
Normally the first item i get is the Meki-Pendant and 2 Health-Pots.

If you got Problems to dodge the spells of Brand, Karthus and so on...
you can start with Boots and 3 Pots (or 2 Pots and 1 Mana). But you lose a bit of your harrass-potential.

Why i dont start with dorans ring?
I will explain it to you. Its a simple reason: because of the sustain.
If you reach level 3 or 4 you can harass your enemy very hard.
After this, take 1 or 2 health-Pots and heal up with your passive.

If your opponent got a dorans ring first, you got an advantage now.
You are (nearly) full again and your enemy must struggle to survive.
There are 3 options,
1 - he get back home and leave you the free farm.
2 - he have to stay at the tower and leave you the free farm
3 - he go offensive and u get a free kill -> free farm

At my first trip back i normaly get boots (350g) and Fiendish Codex (30AP+10%CDR+ManaReg) (735g)
+ 2-3 Pots + 1-2 wards. For the Movement- and the damage + mana-reg-boost.
So ~1200g on your first trip back would be perfect.

The next item is Chalice of Harmony (Manareg./Magicresist) to complete Athene's Unholy Grail.
I love this item!

Ok, i show you the reason, why i get this first (i think this will be the most discused topic of this guide):
You are in Mid, you are a burt-damage-mage, your enemy is (most of the games) AP and you are mana-hungry.
Get this item and it benefits with all of your needs.
+90 ability power
+15 mana regeneration
+40 magic resist,
+15% cooldown reduction (UNIQUE)
Restores 12% of your max mana on kill or assist (UNIQUE)
Increases your mana regeneration by 1% per 1% mana you are missing (UNIQUE)

roundabout: just perfect for you to start with! (and it is cheap, too -> 2950g)


After this you should finish the boots -> sorcceres Shoes. (Magic Pen to do even more damage)
In less games you can buy other shoes:
If the enemy team has got a LOT(!) of CC + AP and you got Problems with the AP/CC on your lane.
-> get Mercury Treads (Magic-Res. + Tenacity)

If the enemy team is full of AD and your lane-enemy is an AD-Champ
-> Probably get Ninja Tabis.

But to repeat: in 90% of my games i'll get sorcceres Shoes.


Ok, which item third? This is not as easy as before.
At this point you have to ask you a few questions:

Can u dominate the enemys?
You got a got farm?
Want to do even more damage?
get -> Rabadons Deathcap 3600g

or

Are you focused and/or died a lot?
Do you feeling to squishy?
You want to slow the enemys (with your W, 35% each target)?
get -> Rylai's Crystal Scepter 3105g

You buy the other item directly after you bought the first of them.

OK, if you cant choose wich item you should buy
buy the Giant's Belt, than get Rabadons and after it finish Rylias.

When you got both items you will be an absolute beast. :)



Then i get the Lich Bane because of the +7% movement speed, Magic Res. and last but not least
his passive. You deal significant more damage if you autohit the enemy between your spells.
You do damage as high as your AP-scale. Its so amazing (because you got ~ 400 AP at this point)
It is not easy to master, but when you do - you will love this item.
If you hit E, Autohit, Q, Autohit, W, Autohit, R, Autohit - nearly every enemy will be dead.
3-4 hits per combo * 400dmg =1200-1600 more damage only with the passive!


The last item is Zhonya's Hourglass. The armor + the active are also very nice.
Against a heavy AD mid, or a fed Karthus i'll get this item early instead of rylias crystal scepter.
I want to see the face of that karthus player, when i kill him and he pushes the R to kill me.
And than i make me untargetable. hehe. If you see Karthus do his ult,
dont panic and do not press directly the shortcut-button(!), u have to wait about 2 or 3 sec!


Another viable choices are a Banshees Veil or a quicksilver sash (if you got problems with CC)
You can get it even earlier, if the enemy team stuns you all the time.

Why i dont get a defense Item like guardian angel?
It is also nice, but i think with your Flash/Ghost and your ulti
+ the rylias crystal scepter slow it is very hard to get to you and kill you.
If you are focused hard, it is better to have one of the anti-cc-items.

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-
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The item build in short:

-- Ap Mid / AP Team?
Athene's Unholy Grail 2950
Sorcceres Shoes 1100
Rabadons Deathcap 3600
Rylai's Crystal Scepter 3105
Lich Bane 3470
Zhonya's Hourglass 3100

-- AD Mid / AD Team?
Sorcceres Shoes 1100
Dorans Ring 475
Zhonya's Hourglass 3100
Rabadons Deathcap 3600
Rylai's Crystal Scepter 3105
Lich Bane 3470
Athene's Unholy Grail 2950

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Ok, there are a few expectations of this item-build:

you can change 1 or 2 items with one of these (sometimes i get one of these, instead of rylias crystal scepter):
Tanky Enemys: Deathfire Grasp (Nice active, late-game item up to 40% of health!)
Many AP Enemys: Abyssal Scepter (if you got problems with an heavy AP Team)
Many AD Enemys: Zhonya's Hourglass (Armor, and a nice active if you beeing focused)
You want CD-Red: Morello's Evil Tome (i dont like it that much, but its not bad)
You Want SpellVamp: Will of the Ancients (Get it, if your team is full of AP, the
extra Spell-vamp synergizes very nice with your passive. Sustain-level over 9000 ;)


If you got Problems early game and dont get much farm: one or two Dorans Ring arent that wrong.
Normaly i skip these to get the core items earlier. But they are a very nice.
Another option is to get a hexfire gunblade for the sustain, but imo 1200g are expensive for it,
if you dont plan to build an early Will of the Ancients.


Ok, to clear the facts:
Like i said, i played Morgana very often as well. I always bought 1 or 2 Dorans Ring, because of the
sustain, AP and mana-reg. But i think the meki pendant and 2 Pots are better for ahri.
Because you can rush the Athene's Unholy Grail even faster.
The Rod of Ages dont fit into my style of playing ahri. The slow from rylias ist much better than the
mana from ROA, so imo never get ROA over Rylias (on Ahri).

Everytime you are in your base, buy 1-2 Wards + 1-3 Pots (only early game, lategame your spellvamp is enough)
I see to often teams how dont buy wards, with a bad support you haven't vision over the map.
This can be an huge disadvantage if you playing against a good organized team!

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Tipps:
Ok, now the interessting part of this guide, the tipps:

- save your ultimate! only use it, when you need it to come away from a gank or to escape a focus in teamfight.
Or use it to secure a kill and you know u wont die (i mean killsecure not steal^^).
When your ult is on cd you loose a lot of your mobility

- If your lane is pushed and you are low in HP, you can use your Q through the wall to hit the Wraiths
so you can get your passive up and heal yourself a little bit.

- You can trap someone: Stand in a bush - E (sharm) - Q (Orb) - W (Fox-Fire) - (perhaps R-R-R)
They will be scared. mid/late-game squishys are dead :))

- If you play against a clever opponent he will be hiding behind minions.
So you cant do the standard combo (like i told you before).
Then try to hit him through the minion-wave with your Q (Orb) and directly with your W (fox-fire).
Now he should be running! Now you can probably hit him with your E (taunt) maybe followed by your ultimate
and ignite. If this is not enough, you probably can do the same combo again (and get the kill)

- try to get the blue as often as you can. Ahri with blue is a motherfuc*ing beast!
Ask the jungler, if u can have the second blue. (some jungler are very mana-dependent [amumu..],
its probably better if he gets the second blue). I like to go with Lee-sin or other junglers without mana^^

- If you see another lane overextend, i mean the enemy is pushing hard:
Push your lane and go (probably teleport to a ward in their back) on this lane to get the free kills.

- The most efficent way to use your Passive (35% Spellvamp) is to do your Orb (Q) into a hole minion-wave.

- i have read the most important (generally) advice in some of the other guides:
1. dont die
2. dont die
3. dont die
4. kill the enemy

Hopefully you get the message, it is better to have 0/0/0 stats, than 10/10/0 !
Be smart, dont be the guy who runs into the enemy team to get the low-hp-dude.


/// i will update the text + formation very soon. And i will add pictures!
Stay tuned. Any questions -> ask me!