The Patch 15 update on October 1 introduced Chaos Siege PvE mode and the Crucible challenge system. Also introduced are a one-handed hammer, new gear options, and cosmetic additions for Season Pass 3.
The announcement separated free game changes from cosmetic DLC. Before purchasing a pass, check what exactly is included in it: the presence of a general update name does not mean paid access to all the listed mechanics. Crucible encourages you to complete tasks with negative modifiers for the sake of progress and rewards. For the first acquaintance, it is wise to first study the normal mode and team composition. A full list of classes that are eligible for the new hammer and reward conditions can be found in the Patch 15 description.