I originally used Riki mid as a direct counter to Pudge. You can build smoke and blink, and if he ever tries to engage on you, you simply drop your smoke and run/blink to safetey. Whenever he leaves middle lane, you simply follow him and gank.

This build is a varient of this, and works well against most heros. Your never guarantued to win mid as a riki. You'll always lose to ranged. Riki will only work as a mid hero to counter a strong gnaker/roamer. NEVER play him agsint a farming mid, such as Clinkz.