The Obsidian Warrior Arena is a PvP map suitable for 2-8 players. Before entering the arena each player should pick some weapons and possibly enchantments and then sleep for the night to set spawn points. There are no set rules how the PvP battle should work. That's something the players have to agree on themselves.
It's a beautiful map with lots of good functionalities which makes setting up a battle with some friends a whole lot easier than having to make an entire arena by yourself.