Hello Everyone 10K here and I would like to share a duplication method that I have not seen since the original Diablo. This is very easy to do and does not take much time.
How to Duplicate Items in Game
Go to the player save file location:
Find the character you are wanting to duplicate all items with. Example: ottar geirleifs.fch
Make a copy of the character file (I normally throw it on the desktop).
Start the game and log into a world with your character (preferably a solo world). Throw everything you have on you in a chest or on the ground. Then log out of the world and shut down the game. (its best to shut the game down so it reloads the character file).
Go back to the character folder:
Replace the character file with the copy you have made.
Start the game and log into the same world as before.(you will have all your stuff back). Pick up everything you threw out (referencing step 3).
Enjoy the duplicates and game.