Leblanc is a strong ap carry with a high burst, very effective 1v1.
She is mostly picked to early gank the other mid hero, she has a hardtime outfarm the others due to only 1 aoe spell and not a high manapool(with my build).
LeBlanc is not played often(at my elo) and I wanna show people with this guide that she is very funny and usefull so we will see more LeBlancs' in the future ! :)

Pros - A high burst, Silence, Good escape abilities.
Cons - Low aoe dmg, Alot depends on the first 15-20 mins.
If she wont get kills early game she will not have high enough burst to one shot their squishy in 1 combo.

I chose these runes because they give loads of ap/magic pen but also some armor, I like armor because you easily 1v1 a caster(even easier when you get banshee) but a ad is harder because they wont get so affected of the silence for example if you face Trynd or Yi 1v1 they will still do high dmg with autoattack.

This is just the normal masteries, 9/21/0 also works, more ap and more surv, but you wont get the extra movementspeed that I like.
21/x/x also works but still no extra movement speed.

Sorc boots - is kinda obvious, boots of swift and mercury threads also works if you meet many melee(swift) or if you meet loads of stun(mercury)
Will of Ancients - I start with that because if you for example meet Annie mid you get high ap very fast because it's cheap, but you also get the vamp that will help you survive a 1v1 against her.
Rabadons Deathcap - If you get it early you can just run around and gank you will One shot combo everyone except their tank.
Banshee's Veil - You already got high ap, you need mana and surv, so Banshee's is a awesome item, also because if you enter a fight you can easily get stunned and bursted down, Banshee will be your help.
Void Staff - You already got surv now you need the Magic Pen to still be able to one shot combo them
Zhonya's Hourglass - The last item that will help both your dmg and let you surv, you enter a fight and you maybe get chased, while you w8 for your blink cd to get off you just use this item and then jump away.

Other good items :
You can also start with the recommended item that gives Health, Ap, Magic pen but I don't do it because you sell it later anyway
Rod of Ages - A usefull item but only give ap, will help you with the mana problem but imo you loose to important stats.

Other bad items :
Archangel staff - It give you mana and ap it's almost the same as rod of ages but rod of ages gives hp also so easy choise.
Meijas Soulstealer - It give you loads of AP, IF YOU PLAY INSANE, so that item is good when you got advantage, I prefer a item that give me advantage.
That item helps in a game when you are owning but it doesn't help you to get to that owning state.

Sigil is most important to skill that's what everyon thinks, but the question is why I chose "E" instead of "W", you can also skill "W" mostly but that's most for farming and I play Leblanc as a ganker so I pick "E"

Ignite - Because the extra burst that is needed, It helps you to own mid early game and to kill their Imba Warwick lategame.
Flash - To survive, your blink spell got very high CD so Flash will help you sometimes.

Other usefull spells :
Cleans - Works if you meet loads of stunners, you enter a fight with "W" get stunnded, uses cleanse and then "W" back
Teleport - To help farm and to gank lanes if they ward in the bushes.
Exhaust - If they got carriers like Trynd/Ashe

Other useless spells :
Ghost - I have seen some people play Flash/Ghost don't do that, ghost isn't usefull because if you wanna flee with it you most likely get slowed and killed anyway.
Clarity - Works but not worth to have, after Banshee it's all ****.

LeBlanc is mostly picked to own their caster mid.
If you meet Annie/Malz or likely, start harass at lvl 2 "Q"-"W"-"W" him and you will dmg, silence and he will loose 2 bars and you will still have full health, but don't be to offensive the creeps may dmg you and then it's not worth it but keep "Q"-"W"-"W" untill lvl 6 and when you reach lvl 6 you should be able to kill him(if you already haven't) "W"-"Q"-"R"-"E" and then "W" back if you get heavily dmg and if she wont die by that just finish her up with Ignite.

I try gank lanes very fast because I don't like farming with LeBlanc due to no farm spells.

If LeBlanc shall be good Mid/Lategame she has to start very good, but if she does she can pick out almost anyone Mid/lategame, but important things to think about in a teamfight is that you shall position yourself good, stay at the side or behind your opponents, if they find you before your tank initate just "W"-"R" and you has escaped, but if they don't find you and the fight starts just go "W" in and burst thier squishy ranged or caster and then "W" back and w8 for spells, don't stand and autoattack(unless you aren't 5v2 or smth)

This is my first guide, please comment and like/dislike, give me criticism and tell if you want guides on any other champion.
And sorry for my english, it's not my home language.
Please discuss with me in the comments because you may make me change some things in here to make this to a better guide.