Hi! My name is MariZika and I'm going to show you how Ive been playing LeBlanc for almost 3 years.
Disclamer: English is not my main language, don't kill me if I make a few mistakes.

LeBlanc is a mage, with a incredible burst damage. Riot changed her abilities, but the combo is almost the same thing 1~2 years ago. My runes and my masteries are kinda different from the ordinary LeBlanc's guide.

As everything, she has really good and bad points, that I needed to put in this guide.

Pros

• She has a really nice scape;
• If you are doing well in lane phase, you will probably win the game;
• Ultimate with a extremaly low cooldown;
• One of the most fun middlelane champions to play.

Cons

• Very banned in low elo ranked games;
• Easy to break the combo if you aren't fast;

Creeping with LeBlanc is hard, I know it. Try your best creeping, if you see is too hard, try going to Top or Bottom to get kills/assists.
Sometimes go to the jungle kill some creatures, just don't make your jungle angry (It's not my fault).

I decided to explain everything here.

Start #1

The start of almost every mage. Stealth Ward will give you extra vision and protection for early ganks. Two Health Potion for some sustain until ~ Level 6 and Doran's Ring for regenerating mana and giving you a little bit of AP.

Start #2

If you are playing against a counter or a self-counter (champions you usually lost playing against OR you hate). Crystalline Flask will help you farming if you receiving too much damage until ~ Level 6. Keep this item with you until ~Level 12. Stealth Ward still can be used, but if you think the other middle laner is warding too much and annoying your jungler, don't hesitate buying a Sweeping Lens.

Essential

Haunting Guise is really good. Why? Magic Penetration and AP. It gives you some HP, because of the runes you will have more HP than the others.
Morellonomicon = Cooldown Reduction + 80 AP + Mana Regen. AND it gives you more damage if the target is 40% health low. A great choice.
Sorcerer's Shoes combined with Haunting Guise and Void Staff (Later in the build) wil give you tons of damage, breaking the enemy defense.

Losing against AP

Abyssal Mask gives you a cool amount of Magic Resist, AP and decreases enemy's Magic Resist. Don't hesitate buying it against Syndra or Katarina.
Athene's Unholy Grail Cooldown Reduction with AP and MP regeneration. It has a little bit of Magic Resist., it'll help you kiting.

Losing Against AD

Zhonya's Hourglass = Armor + invulnerable. Buy it without regreats.

If you're feeling you need extra damage between Mid game - Late game

Void Staff is extremely necessary. The Magic Penetration will add up with the Sorcery Boots and Haunting Guise.
Rod of Ages gives you sustain until Level 18 and a good scale of AP and HP. Go on and buy it.
Rabadon's Deathcap I don't like buying this (actually I never get this late inside a game), but the 30% extra AP with the entire build will give you lots of damage to burst AD Carries and AP champions.

Items I hate buying but you can use

Deathfire Grasp I always forget to use the item, the most important thing about it is the Active. If you are confident about using it, you can buy. If not, Morellonomicon is almost the same.
Mejai's Soulstealer = tons of AP in the Mid game. If you think you are getting a lot of kills buy it before Rabadon's Deathcap.

Skill Sequence you will use almost all the time - -> -> - >

I use Heal + Flash almost all the time. But if you think you need extra damage, use Ignite + Flash.
I know you have two scapes, even that Mimic have no mana cost, Flash is a certain escape, sometimes your Mimic is activated with other skill.

Is good against Galio if you not sure you are going to dodge his ultimate. Use Cleanse against someone with hard CC.
Is viable if your team has a champion with a global presence. e.g. Shen, Pantheon and Ezreal.