Breath of the Wild’s DLC Master Mode will have separate save file 

Worried about having to wipe your Breath of the Wild save file to try out the Master Mode in the upcoming DLC?

Well worry no more as Nintendo has confirmed that you’ll be able to start a seperate save file for the Master Mode. It’ll mean you can explore Hyrule in both standard and Master modes concurrently.

Worry free new game plus.

Source: Zelda Universe