Mobility

How about for most mobility spells (Maybe a few exceptions like Shen because he has high energy costs anyhow), we give them a really high mana cost and give a mana refund after hitting an enemy?

I would mean this only for skillshot mobility spells like Leblanc w, Fizz e, ect...

That way they are punished for using their abilities to run away, and are rewarded for using their abilities offensively, encouraging the high risk/high reward playstyle assassins are supposed to have.

Thoughts?

(Inb4 everyone says this is a terrible idea)