Your challenge rating modifies the strength and number of enemies present in missions. A higher challenge rating will also reduce the number of NPC allies present. When entering a mission as part of a group, the group leader's challenge rating is used.
At the Captain challenge rating, enemies appear with their normal strength and numbers. This rating is appropriate for all players.
At the Post Captain challenge rating, enemies are slightly stronger, and appear in slightly increased numbers. This rating is good for players who are comfortable with their abilities.
At the Commodore challenge rating, enemies are stronger, and appear in increased numbers. Choose this rating if you're looking for more excitement in missions.
At the Admiral challenge rating, enemies are significantly stronger, and appear in increased numbers. Select this rating if you wish to face overwhelming odds, or to make a group mission more challenging.
Switching on your PvP flag makes it possible for you to fight other PvP-flagged players in the Open Sea, even while not within a PvP Hotspot. Any player may attack a foreign player who has the PvP flag set. Flagging yourself indicates that you are willing to fight any and all opponents. You may change your PvP flag status at any Port Captain.