Minecraft wiki entry for Block_and_item_duplication, associated text: There is a way to trick the game into logging in the same player twice on one server. To do this, start two instances of Minecraft. This requires starting a new instance of the Launcher so that they don’t interfere with each other. Log them both on the same server at the same time. By doing this, the game will render two of the same player. You can then kill the copied player and double your inventory. Rarely servers may also duplicate players on accident or leave "ghosts" of logged out players which can be killed for the same effect.