LeBlanc is a great anti carry. If not focused down she can make a game into a 5v4, making someone on their team useless. People will cry op, but she isnt op, you may ask why i say that. After she uses her skills she's usless. Making her not that good in team fights.By the way the first build is for people who are confident in their skills someone who can get stacks and keep them up, and someone who doesnt run out of mana. The second build is for people who have trouble early game not getting stacks, and for people who dont have good mana regen.

Pros:

Great harraser, insane burst damage, Easy Get Aways, her passive can be good if used right.
Cons:

Squishy, After she does she burst she is basicly useless, brands ulti is perfect count to her blink.

Marks:
Greater Mark of Insight is a great rune for leblanc early game.
Seals:
Greater Seal of ReplenishmentGreater Seal of Replenishment is perfect letting you spam your skills early game making you great at harrassing.
Glyphs:
Greater Glyph of Potency in my opinion is better than Greater Glyph of Force because you need the AP early game late game you should be fed enough to not notice.
Quintessences:
Greater Quintessence of Potency for the early game AP.

9/0/21 like all the casters people play.Mage pen Mana Regen and Cool Down Reduction is perfect for LeBlanc.

Teleport:Your squishy so this helps you get back to the battle quicker.
Ignite:This has gotten me so many kills, once you combo they usually get low health ignite finishes them off.
Cleanse:If you are worried about dying this will help you escape when stunned snared and so on.
Exhaust:This will help counter other carries like master yi, making them attack slower, it also helps chasing/running away.
Ghost:I don't recomend this but if you like running fast get this.
Flash:Same as ghost it isn't needed you already have which can be be used again with giving you a total of 2 escapes which is plenty.

Sigil Of Silence
LeBlanc's Passive Mirror Image can be helpfull but it can also be a hinderence, if you dont move it around people will know which the real one is also skills like the bounc around for example brands ulti can easly kill you.
Sigil Of SilenceSigil Of Silence is what does the most damage for her but only if you activate the sigil which is important, when the sigil activates it does more damage and silence's the target.
Distortion is what I use to escape, get in position to combo, and activate Sigil Of Silence.
Ethereal Chains can be good to help you chase people, and it can help you run away, because it slows and after awhile it snares them which can be really helpfull.
This is the bread and butter on LeBlanc, allowing her to do amazing bursts, allowing her to chase, and even escape it casts the skill you used last with bonus damage, at level 1 it isnt that good but once its level 2 it can be really deadly.

For LeBlanc you max out Sigil Of Silence first because its your main damage. Then you max out because you use this skill to escape and activate the sigil from your Sigil Of Silence. Of course you would max next because well its your ulti. Last but not least you max out it isnt your biggist source of damage but its a good snare to keep them in place to combo, or to let you escape safely.

Mejai's:This is a great item for LeBlanc because i find it easy to get stacks with her, and when you get 20 stacks the cooldown is great for her.
Socerer's Shoes:These boots are good for her, some people might get the cooldown boots but I don't see why she doesnt need cooldown she needs the magic pen.
Rabadon's:Well this items obvious it gives alot of AP so get it ;).
Rode Of Ages:This gives leBlanc some survivability, mana and some AP.
Lich Bane:Some people might be wondering why to get this, but its perfect for her if you have enough AP it gives you another nuke which people wont expect.
I don't usually get this but if your running low on mana or think this will help you then by all means get it.

Farming can be difficult with LeBlanc her only good farming skill is which you can ulti other than that she is hard to farm with. She attack animation is really slow making it hard to time, if you have enough mana just spam your .

LeBlanc is by far my favourite champion, amazing burst, great chaser, great at escaping. Using her ulti correctly seperates good LeBlanc's from the bad ones. Once she gets to level 2 she can easly harras. Use your Sigil Of Silence then activate the sigil with causing alot of damage. If they are bbeing cautious and staying far back you can use to get into position folowing up with Sigil Of Silence, just because the sigil doesnt activate doesn't mean it wont hurt. Once you get to level 6 you become dangerous, people wont expect the damage you do.
How To Kill:
Q->R->W->E this is what I use, I use LeBlanc's E at the end because it basicly makes sure they cant escape, You could open up with E but because of its cooldown i dont recomend wasting just to get a combo off. Becareful once you use your skills though, that is when your most vulnerable giving you no escapes or damage.

Hope this guide helps you along your path of become pro with LeBlanc. Please dont vote untill you try this build out. You can add me ingame to ask for advice my name is "ifarmformilk". This is my first build so be honest and tell me if it needs improvements thank you.