If it is true that dowsing targets that exists in other areas have dummies hidden somewhere, then I want to try and find a Zelda dummy
Some targets have dummies.
In lanayru desert there is 2 dummy engines. 1 inside the tower of the building located in the east.
And one OoB behind the entrance to the cave located in the north.
You can also find gratitude crystals inside of buildings in for example skyloft.
An example of this would be inside of the school in skyloft. The dummy crystals in this building can be accessed by getting inside of the building using clawshot vineclipping & the beetle.
And there is dummy actors for the goddess cube chests, one example is a chest that is hidden inside the roof of the bazaar when you're outside.
This chest is a dummy actor for the actual chest located inside of the bazaar.
There is probably more that I'm forgetting.