Stamp The Champs: Kill a champion of all of the following types.
The Stamp the Champs Achievement is a Career Achievement that I happened to earn during Season 3. I completed the Achievement in Hard difficulty and on my Seasonal Crusader. However, it can be earned on any character, at any level of difficulty.
This Achievement can be found in your Career Achievement board under the category called Challenges. It is an Act V Achievement, but I’m pretty sure that I did at least some of it while I was in Nephalam Rifts. You have to kill off Champion packs of monsters that typically appear in Act V in Story Mode.