This guide focuses on using Yi as a very powerful ap carry that excels in early game harassment and teamfighting. He is also able to stay relatively safe in a team fight if he is able to meditate. Ap yi is able to do consistant damage and unlike ad yi can just meditate through exhaust.

Pros:
Able to heal up to full with meditate
extremely high speed for a caster
Able to cause a chain reaction once he gets a kill in a team fight
his attack damage is high for a caster with wuju style
people don't expect you to play ap yi
Alpha strike makes him untargetable for that short duration

Cons:
without meditate he can be killed rather fast
like ad yi he can be crowd controlled to no end
needs to get lich bane unless he has trouble finishing kills
gets wrecked by silences like most ap carries
has trouble killing tanks

Magic pen. marks- It helps to cut through a carries base magic resist early game

Ap per level seals- they are better than flat ap seals at level 6 but they don't really make much of a difference

Flat ap glyphs- gives more ap early game increasing his harassing capabilities and meditate

Flat ap quints- Provides a lot of extra ability power early game

The ability power is for alpha strike I start games at around 40 ap with dorans ring which increases the damage of alpha strike by 40 damage (without resistances)

- Doran's ring is a great starting item for master yi which gives you very nice sustenance in lane with the mana regen, health, and the ability power that helps your meditate.

- An item that let's you harass to your hearts content? What is not to love, it also builds into a very nice ap item a little later. I can see trading this item for a catalyst and building a rod of ages but thats if you need the extra health.

- The cooldown reduction allows yi to become more of a constant burst character in team fights with minimum down time that can be soaked with meditate. I like these boots better than sorcerer's shoes for ap yi, if i need the spell penetration I will just get void staff earlier

- this will spike your ability power and provides a ton of mana regen which pretty much prevents you from going out of mana for the rest of the game.

- this item is a must have for ap yi, this is the difference between harassment and killing. I sometimes have trouble placing this item, I wasn't sure about where this item should go until i decided that after archangel's is about the time where you start to need it. The extra movement speed also let's you chase down low enemies.

- No suprises here, this item turns you into a team killer with the huge ap boost or it turns you into an tank that can't die for 5 seconds without crowd control.

- This item give you a decent amount of health that will allow you survive the aoe burst long enough to start meditating. Becomes less useful if you get a rod of ages so i would replace this with something like an hourglass

- This is your last item, at this point the enemy carries probably have some sort of resistances and this will help you still do a huge amount of damage to them. However don't start focusing the tank just because you have this item.

Items that could work

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- This item gives you two seconds of immunity with a ton of armor and ability power. However this item is often forgotten and in most cases is a pretty weak choice compared to a rylia's but against an heavy ad team with a lot of crowd control go ahead.

- Another very good item that could be used over void staff, this is a more tanky approach if they have a lot of ap carries

- Never used this item but it looks viable against a heavy crowd control team

- I have been starting to move away from rod of ages because it feels like I'm getting it just for the health and I would prefer rylai's in almost every scenario

- I feel like this item is weak, the mana regen is useless at the point in the game where you would get it and the ap is rather low. Ap yi is based on aoe damage not single target. However this item has its occasional use but I'm not really sure about what item it would replace.

-This item has its uses especially against a fast magic resist lane or a heavy tank team in general, however against carries that don't get mr until late game ionian boots are still better.

Items I don't like

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kage's lucky pick- Yi is able to get a great farm early game and is able to maintain that farm all game so I don't see this item ever being useful. If you really are bad at getting last hits then maybe but I still feel this is an item made for someone else.

- ap yi does not need attack speed and ad yi doesn't need ap, unless you are going hybrid i don't see why yi would want these, never tried hybrid yi.

- This is a great item but yi already has an instant full health button so I don't see why he would ever need this

I actually spec into ignite in my masteries for the extra 10 ap to start, the laning phase is a lot about mind games and when you alpha strike+ignite to start it allows you to get minion control fast. Yi with minion control can get a lot of last hits and in the end he needs last hits in order to do the damage. However if you aren't using ignite just switch the mastery to something else.

- This passive is relatively unimportant, it is nice for pushing towers and for getting a lucky kill with the slight boost to your damage early game but other than that it is just a slight bonus

- This move is your aoe damage and your minion farmer. You are untargetable when you use it and it has a chance to instantly kill a minion in lane. Yi is taken to where the target is standing when it ends so he will follow through flashes or blinks. Becareful because if you use it on a champion early game you may get overly harassed and putting you on the defensive which makes you lose last hits.

- This move makes you a tank for 5 seconds if you don't get interupted it gives you an almost unbreakable armor and magic resist (300) and heals you for a ton, this will heal you to full health. this may seem like something ignite can break but even with ignite it steal heals for a ton and gives you the huge armor.

- This is used to proc lich bane and it will give you a decent base attack when leveled up. It is good at pushing turrents.

-This is why he is so viable in team fights, when he gets a kill or an assist the cooldowns on his moves will either finish (kill) or be halved (assist). This turns yi into an incredible team fighter. Just make sure you put highlander on at the right times because if it's not up when you get a kill it could lower your damage in that team fight. Highlander is also good at pushing turrents and procing lich bane

Summoner spells are a personal preference, some of the spells that I don't like are heal, revive, fortify, clairvoyence, rally, and well smite unless you decide to jungle yi

-it is very useful, free 10 ap, scares opponents, 50% healing can be used to ensure a kill on someone even with a support helping them.

- For the most part every champion needs a way to escape, I just prefer flash but I could see cleanse and ghost being viable.

- I could see this being useful when you first start playing AP Yi but don't become to dependent on using clarity.

AP Yi works well with someone who can hold their own in lane and with someone who can stun. Taric, Alistar, and rammus are all good choices but make sure they understand that you need the last hits.

Hit the minion wave with Alpha strike and just last hit like you would any other character. Try to harass with alpha strike but hitting minions and the enemy champions at the same time. Remember the laning phase is about balance, to much aggression and you will die but to little will result in being harassed and loss of minion kills

Be aware that if karthas ults you can meditate to dodge it and should be aware of that at all times. Never waste meditate because it does have a lengthy cooldown and you never know when you may just need it to save yourself from karthas.

If the enemy is rushing magic resistances then I would recommend buying sorcerer's shoes.

In a team fight you want to make sure you want for any enemy ults to pop such as galio, annie, kennen, or ashe because if you are hit by one of those it could spell the end. after it is safe you can alpha strike in, if you are being focused meditate and soak all the damage until they leave you alone or you finish the meditate. Now you want to pick off the carries, Yi is a very good chaser and when he gets a kill he is able to hunt down the rest of the team or is able to do a chain reaction of damage and tanking.

Yi has a lot of utility in team fights and the trick is to understand the best time to meditate.

Now when you are pushing a tower it will be very tempting to instantly pop highlander, however this is not always the best move. Before you pop highlander look around the map and make sure there are no mias, I have been ganked several times after I decided to highlander the turrent and needless to say I had no highlander to get out.

You may say you could get the turrent with highlander and a turrent is worth a death, but if you die you leave yourself open to a counter push and your team maybe unable to protect it because it would be 5v4. Remember the turrent doesn't need to get pushed down right away and that it is very possible for you to later go back and just wuju style it to death.

I hope this guide helped to show how ap Yi can be a big part for any team composition. I actually believe that AP Yi is a more consistant carry than ad Yi because of how much aoe he does and his off tanking capabilities and he also has a much stronger early game than ad yi. He does need a lot of practice and you should understand how much damage you are capable. If anyone has any suggestions or feedback on this build/guide then please post it in the comments.