Unlike most assassins; Ahri's teamfighting (5v5) is much better; because she can harass with Orb of Deception (not easy to dodge in messy teamfights when they're all clumped up), Charm to force an enemy outside their teammates protection (and enable a quick follow up by your teammates besides ensuring a full blast of your Orb of Deception).
Playing Against Ahri
Ahri's mobility is significantly reduced when her Ultimate, Spirit Rush, is down. Plan engages and ganks accordingly.
Stay behind minions to make Charm difficult to land, this will reduce Ahri's damage potential significantly.
Essence Theft (passive) will heal Ahri for its maximum potential when used with Orb of Deception on a minion wave. The passive helps Ahri stay in lane longer than other mid laners.
Orb of Deception is Ahri's main farming and harassing tool during the laning phase. The massive movement speed it grants can help Ahri avoid enemies' skillshots when trading skills.
An ideal early game harassment would be Orb of Deception + an autoattack (which will proc Thunderlord's Decree). This can deal quite a large amount of damage, especially on those who don't have much Magic Resist.
Throw Orb of Deception backward when running to maximize the duration of the movement speed. This can help when running away or chasing an enemy.
Orb of Deception's mana cost is quite high during early game, with a relatively low cooldown of 7 seconds, so it can be tempting to spam this ability which will burn out Ahri's mana very quickly. Therefore, it is advised not to spam it recklessly.
Use the movement speed bonus to steer the Orb on its way back should the enemy attempt to sidestep it.
The movement speed is also useful in escaping ganks when her ultimate Spirit Rush is not available.
It is best to aim Orb of Deception at its maximum range to ensure both parts of the ability will hit the enemy.
When your opponent moves forward to harass you, launch Orb of Deception at them and use the movement speed to dodge their skillshot.
Maxing Orb of Deception is generally best, as it increases the unmitigatable damage in Ahri's kit.
Fox-Fire is Ahri's single target nuke that is best used when at close range to an enemy champion.
At rank 1 and 2, Fox-Fire's damage is negligible and has a long cooldown. However, beyond rank 3 it will start to put a hurt on those who dare to charge into Ahri.
Fox-Fire will proc Thunderlord's Decree immediately should the 3 spectral flames hit the target, thus making this ability a low-mana cost harassment.
Maxing out Fox-Fire first before Orb of Deception is not a bad idea when it comes to extreme melee matchups (e.g.: Yasuo, Fizz, Akali). The secure single-targeted damage (as the ability is auto-targeted) helps Ahri retaliate should they try to engage or juke.
Be wary that using Fox-Fire at close range also puts Ahri into risk of being disabled or worse, bursted down, as she is a squishy champion.
Fox-Fire can also be used to charge up Essence Theft due to its low mana cost or to quickly kill 3 low-health minions (the flame will split automatically if the damage is sufficient to kill the target)
When using your E-Q-W combo, ensure you land an autoattack before casting Fox-Fire to ensure that it targets your opponent and not the nearest minions.
Charm is Ahri's trademark skill and only form of disable. It will only affect the first enemy hit; enemy minions can block it.
Charm has a long cooldown and a high mana cost early game. Take great care when using this ability to trade with your opponent as it will burn out Ahri's mana quickly.
Setting up a perfect Charm for a gank will devastate your opponent,usually resulting in a kill or at the very least force them to use Flash.
Use Flash during Charm's casting animation will result in the projectile fired in the position that you are flashing into. Use this technique will more likely to catch your enemy off-guard than FlashCharm.
Charm can lure the enemy into your turret's range, thus favoring you in a trade.
During teamfights, try to Charm the enemies' carries, which will likely result in their death. Alternatively, you can use Charm to save your marksman(s) from diving assassins such as Zed and Talon.
Charm has a decently long range and the projectile is small. Practice hitting your opponent with it through gaps in their minion waves.
Ahri's ultimate-Spirit Rush is what makes her slippery and versatile. Use Spirit Rush in teamfights to re-position yourself if enemies try to lock you down.
With 3 charges of Spirit Rush and Flash, Ahri can cover massive distance to close or expand the gap with enemies. Often, opponents will burn their own Flash in a futile attempt to escape her; if you know your opponent has Flash, save one charge of your ultimate for it.
Spirit Rush can dash through most walls. Use this trick to create shortcuts when chasing or escaping.
Focus on using Spirit Rush to juke any incoming skillshots rather than damage the enemies as the damage of 3 dashes is still somewhat low unless you are very fed.
Use the 10-second span after your first use of Spirit Rush to wait for your abilities' cooldown then engage your enemies again.
In rare scenarios however, Spirit Rush's damage can be used to finish off low health champions if other skills are unavailable lest they Flash away.
Use Spirit Rush right where you stand (hover the mouse over your champion) to deal the immediate damage from Spirit Rush without putting yourself into an unfavorable position. Use this technique when your E-Q-W combo doesn't deal enough damage to kill your target.
Flash can also be used in the same manner with Spirit Rush, simply Flash mid-dash (or Flash and Spirit Rush) will fire the bolts in the new position, thus dealing damage to any outranged enemies.
The best use of Spirit Rush comes with reaction time - if you can react to your opponent's aggression in time, you can turn it against them. Many midlaners rely on landing their combo as quickly as possible, like Vel'Koz and Zed. Dodging their all-in combo plays leaves them completely open to Ahri's return aggression, resulting in an easier kill.
Thunderlord's Decree is generally the best Keystone for Ahri, as one spell combo in lane will proc the mastery, adding more damage to her mid-late game burst combo as well as giving her more assassination potential.
Rylai's Crystal Scepter is no longer an excellent item for Ahri; while much of her kit involves kiting around enemies and dodging skillshots, the slow is too weak to make much of an impact in duels, and it does not scale as well into the late game. While it can be useful if you are pressing an advantage, Luden's Echo is usually a better buy, as it greatly enhances her all-in potential.
Zhonya's Hourglass will mitigate any source of physical damage, the extra armor is precious as it complements to the already-low base armor of Ahri. The active from the item will likely neutralize all physical (and even magical) burst, namely Zed'sDeath Mark and Syndra'sUnleashed Power.
The former is useful when the enemy team has lots of sustain or when you need more CDR while the latter may come in handy if the enemy team has squishy carries who are going to build MR to counter you.
Ahri is quite flexible when it comes to boots choice. She can also buy Ninja Tabi to fend off heavy physical damage dealers such as Yasuo and Zed. Likewise, she can equip herself with Mercury's Treads to counter devastating Crowd Control effects and heavy magic damage dealers like Veigar or Annie.
Cooldown reduction is helpful on Ahri, due to her being a combo mage/assassin - having your abilities available more often not only increases her DPS in teamfights, but also her survivability with Spirit Rush.
Keep in mind that once you have maxed it, Fox-Fire will deal massive damage to squishies. If they build magic resist, counter with a Void Staff.
Luden's Echo is a great item to get early if you are doing well and roaming, but keep in mind that you will lose some of the early utility gained from a Rylai's Crystal Scepter.
Combining both Rylai's Crystal Scepter and Luden's Echo will gain a massive amount of AP and kiting abilities to burst down carries or to deal with fighters/tanks. However, these 2 items are quite costly and do not provide any mana regen or CDR, which are also important to Ahri.
If the enemy team is stacking health to counter your true damage, Liandry's Torment is an acceptable choice. Combined with Rylai's Crystal Scepter, they will grant Ahri a large chunk of extra health and percent health damage. As a bonus, Liandry's Torment features a nice piece of magic penetration.
Consider building Liandry's Torment over Void Staff if the enemies, especially key targets, don't have any much MR-i.e., the amount of Magic Resist is under 50 as you can completely negate their whole defenses, dealing nearly true damage.
Lich Bane can add a surprising amount of damage to Ahri's burst, provided you can find a moment to land an autoattack. It also offers mana, movement speed, and cooldown reduction, which are all very useful stats for her.
Lich Bane goes well with Luden's Echo in terms of bursting power. This build is extremely effective to one-shot annoying and slippery champions who are likely to sidestep to dodge nearly all of your skillshots with their huge movement speed boost like Kalista, Ezreal, Zed, or Yasuo.
Lich Bane will proc with each cast of Spirit Rush. Carefully weaving autoattacks and spells will result in extreme DPS.
Ahri does not have a very high burst by herself unless she is ahead, so avoiding her skillshots will cut her damage exponentially.
Banshee's Veil can provide protection against Charm which is key for Ahri to maximize her damage.
Side stepping her Orb of Deception, especially on the return damage, is pivotal to win the lane against Ahri.
Keep track of her Spirit Rush charges in skirmishes and team fights. Avoid wasting summoner spells if she has all of her escape options available. You can tell if she has dashes remaining by the swirling lines around her feet.
Stay near minions all the time will greatly reduce Ahri's bursting power as they will cover Charm, absorb a portion of Fox-Fire and Spirit Rush.