Everything and everyone in Uri Nanna has a soul and when something dies it's soul is taken to another place. It may become a part of this world again or join Tiamatu the river of souls. But there are cases of souls going missing along their way. The Marionette is a different matter. A reverse process if you will. In simple words a Marionette is the unity of a soul and a construct. These creatures are a rare sight and don't become a part of this world by natural means.
The simplest form of a Marionette is a soul trapped within a training dummy. From the outside they look as they were before but on the inside is just a dummy. Another way of looking at it is a doll wearing a humanoid costume. While the Marionette is healthy it looks as it did before dying but as it starts sustaining injury it's features start to become more and more translucent until there is only the dummy.
The Marionette does not know that it was dead before or what it is now. They may only have a gap in their memories from the point they died until a few hours after becoming a Marionette. For that reason it lives it's life as any other would. While it does not need to eat for any physical reason it still eats. That same pattern goes for anything it did in life. If a Marionette stops eating or sleeping it's sanity starts to deteriorate until a day when it goes fully insane. This fate can happen faster if a Marionette learns what it is but until then it rationalizes any abnormality.