I ran from Darius in a DARIUS v DARIUS and got stomped
You don't runway from Darius you sit on him and you laugh that his Q does nothing to you and nothing for him. That's right, to counter this melee you stay in melee range. It's very unintuitive and very daft but that's how this is. It took me a Darius vs Darius to understand his 2nd flaw: you want to get close but not too close, none of that touchy feely stuff in Noxus apparently.
