Your inventory will stay the same, but your chapter progress is reset. New Game+ is unlocked after you complete the game once. Completion unlocks the MK-II Overclocked Parts Set and a Mega Resource Deposit. I hope this information helps someone because I looked for a while and could not find any information online about this.Enemies only drop resources, and there's no ammo, health, or weapon parts to be found. That is the first time all of your unlocks become available. Using this method, you will not be able to use the Devil Horns(or any other unlocks for that matter) until you reach Chapter 3 and power on the workbench. Tell it to use cloud saving anyway, which will just keep the 360 from importing your old save back to the Xbox One again. It will also likely ask you about your pending cloud save. You will want to say somewhere else and allow it to import your cloud saves. When you log back into your Xbox One profile, it will ask which console you played last on.You can now exit game, go back online, System > Storage > Internal HDD > Copy the new save slots to cloud storage.If the message 'Devil Horns unlocked' appears when you make NG+ game save, then you did it right.

Be sure to save them in slots that are empty on your Xbox One copy of DS3. Make New game + of both Survival and Hardcore.Disconnect from the internet, and while in Storage, press Y to clear System Cache.

Log in on an Xbox 360, then go to System > Storage > Cloud Saved Games > Copy a save file that has Devil Horns unlocked to the internal HDD.

Make sure your Xbox One save data is on your save data cloud.

I've seen people asking if this is still doable on Xbox One, and while it is not, you CAN transfer your Dead Space 3 save data FROM your Xbox One to an xbox 360 and do the above method. Now, many people know the old trick on Xbox 360 where you could clear your cache and load the game in offline mode, which would unlock the Devil Horns on Hardcore and Survival, since it was available before it had been patched out. In Dead Space 3, the Devil Horns you unlock in Classic mode are not able to be used in Hardcore or Survival normally. I thought I'd share this since the next most relevant post is 6 years old.

Dead space 3 devil horns save file pc