The new Zodiac system is a progressive challenge system, in which players can challenge Zodiac Guards and Gladiators from weakest to strongest. Higher-level Zodiacs have stronger NPCs, as well as better rewards.
Periodically, Elite Zodiac Guards will appear in the Zodiacs, who will drop rare, high-quality items if defeated. However, there's only a limited number of Elite Guards to defeat every day.
You can earn Zodiac Tokens when fighting the Zodiacs, which you can exchange for powerful equipment and other items.