Kill Champions Easily with Necromancer:
After you have gotten the Bone Prison ability, you can use it to great extent to defeat most champions. Cast Bone Prison around an enemy SEVERAL TIMES and then use either Bone Spear or Bone Spirit on the enemy you have imprisoned. if your Bone Prison is a high enough level, the enemy won't stand a chance of breaking through all your Prisons in time. This tactic is effective all the way from Normal Act I enemies all the way to Hell-Difficulty Mephisto (with the exception of Nightmare Diablo and Nightmare Baal, because their attacks shatter the Bone Prisons too quickly. To defeat those enemies with a necromancer, just run around casting Bone Spirits.).
Thanks to GR reader A.Morace!