The Duellist's cap is a hat that keeps track of the amount of kills in the Duel Arena of the wearer. The tier 2 cap shows that the player has won 10-99 duels. If a player gets 100 Duel Arena kills, they can turn it into a tier 3 cap by clicking Change-look. Together with the Wildstalker helmet, this cap will give the owner the ability to transform into a statue, which shows various PvP stats. It gives access to another emote, which lets you take off the hat and bow. This emote can only be done every 15 seconds and requires a clear area around you. There is currently a glitch with the "Brag" option, where the Cap seems to turn slightly darker.
In the chat interface, only one of the magenta jewels on the front brim of the hat are shown, when there are actually three.