IntroductionIrelia is a solid counter-carry. Her primary role is to shut down and threaten squishies in the back with her insane mobility and burst. She is much less gimmicky then Akali or Poppy, two other champions that share the same role as Irelia (counter-carry, mobility, burst). Meaning if you enjoy playing Akali and Poppy, you will see much greater success playing Irelia.
Masteries0/9/21 is the only Mastery build I would ever consider. Presence of the Master is a necessity. Strength of Spirit gives you the little bits of HP regen you need while laning. Meditation is also necessary to keep your Mana up while using Q to creep. 6% CD, 3% Movespeed, 6armor/mresist are all excellent.
Early GameYour primary goal is to farm. You will find yourself last hitting at tower often, so be comfortable doing so.
When you reach level 6, clear the wave with your ultimate and buy items(get a ward!). Since Irelia is such a strong duelist, I recommend farming your lane for at least the entire duration of early game, scoring a kill whenever possible, otherwise harassing them out of lane with Bladesurge and Equilibrium Strike, or perhaps just farming passively.
Mid GameSince you're most likely farming top, I don't recommend fighting any teamfights until you have at least a Trinity, if you choose to rush trinity then get red and hope your enemy engages on you.
Irelia's mid game is generally still just farming top very effectively, at this point you should have 1-2 gold/5 items, just sit on those and cs as well as possible. If your lane partner leaves top to pressure dragon, either follow or kill their tower, and make sure your team doesn't engage them at dragon if you choose to do the latter.
Towards the end of mid game you should have your Trinity, this will give you insane mobility and burst. Score kills with ghost/ignite and play passively when they are down.
Late GameIrelia is insanely strong once she gets 5-6 items, she becomes near unkillable. With FoN and Trinity's movement speed, Irelia moves at near 500 MS. At this point, Irelia should be actively engaging in fights and initiating for her team. Choose your fights wisely, take advantage of your deceptive tankyness and burst.
Team FightsIrelia's goal in teamfights is to kill the squishy. But if you can't kill them, it's not a big deal as long as you pressure them. A Ashe that is scared of being bursted cannot stand still and auto attack when Irelia is still in the middle of the fight, with just Irelia's burst presence, she can nullify a lot of auto attack damage from AD squishies.
Irelia's ultimate does surprising amounts of damage in teamfights if the enemy groups up, with the short cooldown, always look for creep waves to heal yourself then somehow get back into the fight.
The longer the fight drags, the better it is for Irelia, since Equilibrium Strike is on such a low cooldown, being able to stun multiple times can be game breaking.
RunesThere are no better alternative to the Armor Pen marks.
Consider HP/Level seals, but due to the HoG changes, the flat Armor is really sexy early.
MR/Level glyphs are the strongest glyphs.
Consider Flat HP, Movespeed and Flat ARP Quints. The 8.1 Hp/5 from quints is very powerful, however if you don't need the Regen or maybe not even have them, 10 ARP and 4.5 Movespeed are also very strong.
Ignite is very important. It synergizes with her burst and makes laning against her very scary.
Ghost is better than Flash because Irelia can sustain herself in the fight to take full advantage of Ghost duration. Ghost also makes Irelia practically invincible, able to escape from 2~3 man ganks with her passive.
Passive: Ionian Fervor
Each nearby enemy champion (to a maximum of three) reduces the effectiveness of Crowd Control on Irelia.1 Champion: 10%2 Champions: 25%3 Champions: 40%
Irelia's passive is insanely strong, the CC reduction makes Irelia almost impossible to lock down, making carries very uncomfortable when they are playing vs an Ireila. Knowing the limits of the CC reduction is very important for Irelia players, since as long as Irelia remains in the fight, at 50% hp, 30% hp or 5%hp, she can still burst down a carry and remain a threat.
Irelia dashes forward to strike her target for 20 / 55 / 90 / 125 / 160 (+1 per Attack Damage). If it kills the target, Bladesurge's cooldown refreshes and refunds 35 Mana.
Cooldown 14 / 12 / 10 / 8 / 6seconds
Always try and use auto attacks to creep, unless you want to creep faster, or cannot creep unless you need the extra damage. At early levels, 1 auto attack and tower hit along with a Bladesurge kills the ranged creeps in the back.
With Sheen, you can Bladesurge and kill a ranged creep, allowing you to engage on squishies that are playing very passively.
At level 5, Bladesurge's cooldown become insanely short, which is another reason why it's so uncomfortable to play vs an Irelia as a squishie, you can assume Bladesurge is almost always up.
W: Hiten Style
Irelia is skilled in the art of Hiten, passively giving her physical attacks 10 / 14 / 18 / 22 / 26 health restoration. Activating Hiten Style adds 15 / 30 / 45 / 60 / 75 true damage to her physical attacks for 6 seconds.
Consider maxing Hiten Style first if you're guaranteed auto attacks on your enemies, mainly tanks.
Gaining hp on hit makes Irelia deceptively durable.
Synergizes well with attack speed.
E: Equilibrium Strike
Irelia's attack balances the scales, dealing 80 / 130 / 180 / 230 / 280 (+50% of ability power) damage and slowing the target by 60% for 1 / 1.25 / 1.5 / 1.75 / 2 seconds. However, if the target has a higher Health % than Irelia, then the blow stuns the target instead.
Cooldown 8 seconds
Cost 50 / 55 / 60 / 65 / 70 mana
Allows Irelia to be deceptively strong.
Can survive ganks by timing Equilibrium Strike for the stun.
2 Second stun is a long long time.
At level 5, Equilibrium Strike does considerable damage.
Equilibrium Strike makes Irelia a threat as long as she remains in the fight.
R: Transcendent Blades
Irelia summons 4 spirit blades which she can fling at her enemies. These blades deal 85 / 135 / 185 (+40% of ability power) OR +0.6 per bonus Attack Damage magic damage to enemies that they pass through, and she heals for 20% of that damage.
Cooldown 60 / 50 / 40 seconds
Cost 100 mana
Can clear creep waves, however you will need the bonus AP from Sheen to 4 shot back creeps at level 8-10.
Gives you great laning sustainability.
Does decent damage, which synergizes with her burst.
The heal makes Irelia deceptively tanky in teamfights.
The cooldown is short, don't be afraid to spam!
Skill OrderMax Hiten Style first for laning domination. 75 True damage at level 9 makes you a huge threat.
Then Bladesurge to lower the cooldown so you can chase down squishies midgame.
Lastly Equilibrium strike.
Final CommentsRemember your role is of an assassin, however your survivability matchs that of a bruiser. Push Irelia to her limits by maximizing her insane survivability in teamfights and try and stay in the fight as long as possible. Irelia's greatest strength is her presence in a teamfight, knowing how to abuse this presence and fully utilizing her passive and self healing to the extreme is what every Irelia player should strive for.