PVP
PVP is turned off in the main worlds (overworld, nether & end), however you can fight other players within the PVP Arena.
To access the arena, you can use the command /pvp.
Keep Inventory is enabled within the PVP arena.
Upon entering the pvp arena, you will have to drop down to enter the fighting zone.
Upon being killed in the pvp arena, you have a chance to drop a head with your skin. This head is purely cosmetic and doesn't serve any purpose other than being your skin.
Example of a head dropped from killing a player in the PvP arena.