Hey, simple & short: Found the Designerlevel.
What does it include, what does make it special?
You will find alot of zombies (about 50-75) with Designer Names. An Example:
Michael Chu
Game Designer
You will find one Rarmob named Jay Wilson, which rewards you with a FoS after killing him.
If you dont know Jay Wilson, he is the Game Director of Diablo3.
Imagelink: https://i.imgur.com/RnNjC.jpg
How to find it:
Get the Quest "Shattered Crown" (Act I , Quest 2 (or 3))
There will be 3 Crypts & one CAN be the Game Designer Level.