This glitch lets you double any item you want, as many times as you want. All you need is 2 players and a chest.
Step 1: Get a Friend to Play With You.
Step 2: Put What You Want to Double in the Chest.
Step 3: This Is the Tricky Part. You Both Need to Click the Item at EXACTLY the Same Time, and If You Did It Correctly, Both of You Will Have That Item in Your Chest.
Step 4: Put the Item in the Chest and Repeat As Many Times As You Like!