Essences:
Essences allows you to perform manipulations in the game such as changing an entity, editing the last story turn, and taking an “open-ended” turn.

• Essence of Transforming: Allows editing name/description of 1 entity
  
• Essence of Rewinding: Allows editing the last story turn
  
• Essence of Opportunity: Allows 1 “open-ended” turn
  

Essences have a chance of dropping from regular mobs, at least 1 guaranteed drop from an elite mob, and 1 of each will drop for a legendary boss. Your max # of essences is influenced by your character level.

Creative mode:

In creative mode you can do all these things infinitely without needing to consume essences. This can be toggled on or off at will in the options.

Misc:

There was an issue where the save would be corrupted if your follower became an enemy and died in a place they weren’t born. This is probably fixed now.