Myself and a fellow D3 player located it. Here's a video of the action. It appears that it's similar to finding a goblin, while most of the people reporting that they've found it in Act 1 in various places. We did it while simultaneously doing bounties for a bit of extra reward.
https://www.youtube.com/watch?v=6ol2wBG86yM&feature=youtu.be
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This involves the use of The Furnace or Maximus, Hexing Pants of Mr. Yan for extra dmg and Fury building, Tasker and Theo for pet attacks, and a Cindercoat to help supplement Fire dmg and resource cost reduction. Let me know what you all think of ways to improve this build, whether it be for more damage or survivability (yes, I need better optimized gear).
Video guide and gameplay:
http://youtu.be/PJIZUnqPd30
Skill setup and gear:
http://www.diablofans.com/builds/6744-the-ancients-firewhirl-build
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(links removed)
Feel free to check out both of our channels for lots of Diablo 3 content as well. Thanks to all!
-JHow