Obsidian Destroy or Outworld Devourer is one of the strongest mids in the game yet so many people fail with him because they build him wrong. Arcane Orb doesn't scale as well as your passive and disable guys.
Also when in lane remember to spam Astral Imprisonment, use it to distrupt last hits which will drive people especially melee mids insane, while making it easier for you and harder for your enemies to last hit if they are intelligence. This build also contains a contingency if you're having problems.