I did some testing with hidden mashine and here are my conclusions. I tested the following situations:
- The enemy is idle, has not noticed me
- The enemy is attacking me or is repositioning
- The enemy is attacking my pet or is repositioning
- Fade Away: The enemy is attacking the ground, where I was standing when Fade Away started, or is repositioning to attack the ground
Hidden Mashine works in the situations 1 and 3, but not situation 4, which is clearly a bug.
So, if you want to trigger Hidden Mashine, try to create the situations 1 or 3. However, sometimes it is difficult to determine, why the enemy is repositioning. It can be situation 2 to 4.
Without Fade Away, it is difficult to create these situations and trigger Hidden Mashine. So it is probably worthless in Rakk builds.