This is the first time I am doing a guide on Mobafire, so the style of the page may look weird. Please don't punish me for that.
I have played League of Legends for 2 years now. One of my main is Irelia. The normal build of off tank dps is all good, but we should try another new way of playing. You never know, maybe it will become the new standard build! Hope you like my build for I personally find it working.

This build is for Attack Speed Irelia. Your W will be the main skill. The goal of this build is to achieve 2.5 attack speed. When you open your W, you regen crazy health while doing tons of damage (true + normal attack damage + item damage if any).

The guide has been edited from before, after I saw my first comment, I realized that this build is not an ad carry build and hence does not need full ad carry masteries/runes/etc.

Pros:
- Insane damage if you get your way.
- Kill tanks pretty easily too.
- People may intuitively think you are going off tank dps and if they didn't notice, they may avoid focusing you first.
- At the three elixirs and blue buff, or maybe even earlier, you can solo baron in half a minute.
- Very good sustain as a carry for the heal on W, and the full defense runes and defense masteries
- Can duo lane and solo lane -> good sustain and defense, but the build does not require as much gold in early game as Offtank.
- Has a natural stun/slow that many normal carries don't have and you can use your stun/slow often than other carries that have a stun skill.
- Q is a good escaping/chasing skill if the position of enemy creeps is good.

cons:
- If in duo lane -> possible loss of farm
- Relatively squishy compared to off tank build.
- If they notice you, the the third pro won't be there and you will be treated as a normal carry and be focused on.
- With passive but no tenacity boots, you are relatively more susceptible to disables. Once you are disabled you can't do anything and since you are a carry, you get killed easily (but the same applies to almost all carries).
- Q require good condition, otherwise no natural escaping mechanism.

The runes are selected to max the amount of armor/magic resistance in the amount of runes that you can use.

I personally dislike the per level runes (hence I cannot understand why some people suggest them), because in my mind, if at level 18, the armor obtained is similar to the flat armor runes, then why not have the flat armor at all levels?

As an alternative, for I personally prefer to stack Magic Resistance (MR), if the game allows me to choose between Armor (AR) and MR that is, hence my runes are mainly for armor. However if you find yourself like the armor in=game items more, then I suggest you purchase the flat magic resistance runes on all slots instead.

As said in intro, I find that attack speed Irelia does not need to go full Attack damage mastery. Hence I have taken full points on the attack speed mastery in offense, but put the rest in defensive masteries to max the sustainability in lane and battles.

Since the build is for attack speed and not attack damage, there is no need for armor penetration on the offensive mastery tree, hence the offense mastery stop at 4 points in Alacrity and the result combination is 8-22-0.

The items' purpose is pretty straight forward: to get 2.5 AS. Madred's Bloodrazor allows you to kill tanks (as a normal ad carry should) and the Phantom Dancer get you fast to 2.5 AS while you get also great mobility (which is also important as a carry because you need to be at the best position in team fights).

I originally had a third Phantom Dancer instead of the Black Cleaver until a recent game when I realized that the cleaver will do a better job. Hence I have replaced the third Phantom Dancer with Black Cleaver.

I suggest Ignite and Flash for a regular buster spells.

However, I also recommend the following:
Suggested Choices:
Ignite: a good finisher, you never know when the enemy will run away with 35 hp.
Flash: even though nerfed, still grants considerable amount of escaping mechanism.
Ghost: a good spell to replace Flash, advantage is that you can chase people and run with it pretty well; the disadvantage is that you cannot ghost through walls.
Exhaust: since you are a buster, you want the main output of the enemy team to not able to kill you before you kill your target (which is often the main output of the enemy team), you want to have exhaust by your side.

Possible Choices:
Cleanse: since you are not taking Mercury Trends, you are relatively more susceptible to CC, hence Cleanse may be a good option.

Don't take:
Clarity: if you have problems with your mana and it is affecting your game play, you are not using Irelia (offtank or attack speed) correctly.
Heal: your W will give enough health back.
Promote: not for a carry or offtank.
Clairvoyance: this is for supports in general.
Surge: the attack speed is nice, but not significant and it requires that you will be hitting your target. But your target won't just stand there. I personally think this is a bad skill for normal games.
Revive: only champion that I would ever suggest revive is Dr. Mundo for many reasons, details you can find at the video from SivHD:

Hiten Style - activate in 6 seconds will grant double of original healing effect and true damage. This build maxes this skill first, because that is the core of this build for you want to hit as many times in that 6 seconds.

Equilibrium Strike - use on close range enemy will stun (if your hp is lower), or slow (if your hp is higher). This build maxes this kill next because the stun is awesome, and slow is good for chasing.

Transcendent Blades - shoot out blades in front of you, damage all in contact and heal you by percentage of damaged. Always level up your ult whenever you can, it is a good chasing skill (remember you can move while using your ult) and also good farming skill for the short CD.

Bladesurge - Close gap and deal damage. If target dies part of mana is refunded. Even though it is the skill that has 100% AD, this build is not technically AD carry, more like AS carry. So all you need is to use it for last hit minions or closing gaps so it is not necessary to max it first.

Unlike champions like Wukong, Irelia doesn't have as many combo choices.

Due to the required condition for your Equilibrium Strike, it may be good to wait until you take a few hits before you engage in battle as the 2 seconds stun on the right enemy can completely turn the battle to your favor.

It is known old combo that you shorten distance with Bladesurge, taken some hits, use your stun on E, then open up Hiten Style and kill your enemy (usually squishy carries) in 4 seconds. If they start to run, make sure you are moving towards their running direction and use your Transcendent Blades at the same time. It shoots towards the location of your mouse, so it is also easier when chasing the enemy.

When you are running away, it takes some more micro skills, but you can move your mouse to your back, use R, then move the mouse back to your front, direct movement, move mouse back, R, and back to front, and so on and so forth.

Always use your R when running away as it gives you life steal and great damage that makes your enemies back off.

This build is not intended for jungling. And Irelia's passive is not being used in jungles.

Since you go duo bot with a tank/support, especially after Madred's razor, you should be able to farm quite good.

Use your Bladesurge well as it is the best last hit skill, it gives mana back if you do kill a creep too. So it is self sustainable.

Farm as you wish, but don't push (remember you are in a duo lane. There is no benefit in pushing, unless of course you need to recall, then you push and go back).

I remember a pro player once said: "If you are smart, you would let your turret (unless you are mid or solo top) be pushed really early so that you can hug all the farm by using the lane clogging. Play Video

You are not an off tank or tank anymore, so don't rush up front.

Wait for your chance, close gap with Bladesurge if necessary, otherwise save it for chasing or escaping since it is your only possible escaping skill.

Fighting in jungle is better than in open because you should try to find a 1v1 fight whenever you can. Your Hiten Style and Equilibrium Strike will kill them faster than they expect.

If must fight in open, use your Equilibrium Strike on the right person, don't only focus on your victim. Remember if you don't stun somebody else when you should, that person may affect your fight with your victim so that person is part of your fight anyways. Keep your eyes open.

Help jungler gank mid whenever you can from bot. Your Q will bring the ult-most surprise on their mid squishy champ. And when your jungler is ganking your lane, save your E for the optimum moment.

Your greatest advantage is your true damage on Hiten Style (which is also part of the reason why Riot keep on nerfing Irelia, it is also one of the reasons why Ahri is considered as op in certain circumstances).
And we are maxing that advvantage in this build.

Your next great advantage is your passive Ionian Fervor - up to 40% reduction in CC effects. This passive and Mercury Trends (if you get it) makes you almost invincible to CCs.

Your W also brings crazy health regen, better than Xin Zhao's passive if you get full 6 seconds to hit (of course the best drain skill is Fiddlesticks' Bountiful Harvest, omg can even drain Vladimir when he goes into Sanguine Pool).

Offtank Irelia is good and all, but try something new once in a while.
Remember your role as a carry.

Hope this build works for your style. Have fun and go pwn your enemies!