So I had the Mysterious Cave as a Bounty, and I noticed that on Level 1 there was no Mysterious Chest, which as you know offers only a single vial of Liquid Rainbow, one of the ingredients needed to build the Staff of Herding:
https://us.diablo3.com/en/artisan/blacksmith/recipe/staff-of-herding
- Black Mushroom
https://diablo.fandom.com/wiki/Black_Mushroom
- Leoric’s Shinbone
http://us.diablo3.com/en/item/leorics-shinbone
- Wirt’s Bell
http://us.diablo3.com/en/item/wirts-bell
- Liquid Rainbow
http://us.diablo3.com/en/item/liquid-rainbow);
- Gibbering Gemstone
http://us.diablo3.com/en/item/gibbering-gemstone).
I have never actually built a Staff of Herding, because I have no interest in endlessly farming Whimsyshire (corrected ty to MB). But if the ingredients present themselves, I collect them. I have never possessed all of the ingredients needed to build the Staff of Herding at one time.
As it turns out, like all other things, the Mysterious Chest on Level 1 of the Mysterious Cave is not guaranteed, but a random spawn that may show up. So there wasn’t one in my game, but it was a serendipitous occurrence that gave me the opportunity to refresh my memory and to convey the foregoing information to others who may not know it, or whose memories may have dimmed over time.