Codex Arena, also known as Sealed Deck, is a fun and challenging PvP game type where players create builds from a limited pool of skills. Here's an overview of the new format.
Create a Team
Form your own 4-player team in the Codex Arena outpost (formerly the Hero Battles outpost).
Only one of each primary profession is allowed on your team.
Choose Your Skills
In the outpost, open the skills tab and select from The Codex—the list of skills that are currently available for your primary and secondary classes.
You can choose from 20 skills per profession—15 regular skills and 5 elite skills. Players may only choose elite skills from their primary profession.
The Codex
The Codex is the list of skills that Codex Arena players must choose from. To keep things interesting, we'll change the skills in The Codex each day at 12:01 AM Pacific (7:01 UTC). When The Codex changes over, we'll let you know by sending a chat message to all players in the Codex Arena outpost.
If you're playing a match when the daily skills change, you can finish your match. Once the match is completed, you will be sent back to the outpost, and must select from the current day's skills in The Codex before playing again.
here is what it says on gw web site, i'll try and have a play tonight
The Codex Title
To accompany this new game type, we've introduced a new title track for Codex Arena: the Codex Title Track. The Codex Title replaces the retired Commander title from the Hero Battles format, but still retains its counterpart in the Hall of Monuments and counts towards earning your Kind of a Big Deal title. What does this mean? If you've already achieved the maximum rank of Commander, you won't be required to achieve the maximum rank of Codex to earn or maintain your Kind of a Big Deal title. If you haven't achieved ranks in the Commander title, you can work your way up the ranks of the new Codex title.
For those seeking to fill out their Hall of Monuments, we've introduced a new Codex statue to add to your collection. If you achieve Codex rank 3 or greater you'll receive the Eternal Codex Disciple statue to place on your Monument of Honor in the Hall of Monuments.