I have the Blade. I want the achievement. And besides, Bashiok is a smug jerk and killing him would be satisfying.
I know he's a rare spawn, but what kind of mob is he a variant on? In which chapters, zones, and difficulties can he spawn?
Bashiok is a rare Fallen Shaman mob who can be randomly found (or not found) In Dalghur Oasis and the unique title: "Death is not the End".
If you're not satisfied after killing him in game, you can also hunt him down on twitter.