Le Blanc is a perfect mid character with she's silence and the quick escape abillities.
Sigil of Silence is a great abillity with it's silence and heavy damage, combinated with Distortion.
Le Blanc is a great assasin who can hunt or just nuke down champions with a incredible speed.
Le Blanc is a perfect 1on1 character with it's heavy singel target damage, the perfect assasin slayer.

Not much talk about the runes, it's designed for heavy damage.

I chose ghost and ignite for the extra damage on ignite and the great speed for chase or fleeing.

For items I chose heavy early damage.
Soul stealer is a great item for Le Blanc who get kills easy with and without ulti.
Rabadon helps alot to stack Soul stealer up early for the damage in late game.
After Rabadon I go more defensive with a Banshee's Veil because of the great passive but also for the hp and extra mana.
I keep going for the damage and getting a Void Staff for the magic ress champions and finish of with a Crystal Scepter for the extra hp and hp.

Pros:
-Heavy damage.
-Deals tons of damage in some secs.
-Great fleeing skills.
-Slow and rooting spell
-Great ganker

Cons:
-Can't handle much damage.
-When abillities on cd she is very weak.
-Often targeted
-Almost needs to be a little bit feeded to work as wished.

Le Blanc got a deadly combo:
Q -> w -> E who deals high damage and rooting the target in place for next rotation and most likely the target is probably on the run after the damage so it is just to finish of the champion.
When ulti is up:
Q -> R -> W and if nessesary E if the target isn't dead.
The combo can variate on different situations.

Le Blanc is a great champ with a lot of damage and a great fleeing skill.
She is really deadly and can slain even the most feeded champions if she has some abillity power.
Great on entering battles and turn the fight into the right deriction!