This guide is built specifically so you can own people at bottom lane. You are the ADC, so you take good tanky supports such as teemo. The summoner spells are taken so that you can jump in like a sneaky ninja and steal cs with your OP smite. Also, ghost is necessary so when you get super fed, you can catch up to people and pentakill.

I like to take wall of pain maxed out first because it slows your enemies. This allows for you to spam your basic attacks, doing a whopping 100 damage per hit. His Q scales on AD, so I max that last.

I take all attack speed and lifesteal items because they are OP. You need to take advantage of the OPness of the Runaan's before it gets super nerfed by Activision.