https://www.gamespot.com/articles/destiny-2s-the-dawning-event-adds-snowball-fights-/1100-6455661/

Destiny 2 did not have a Halloween event this year, but the game will celebrate the holiday season with a winter-themed makeover and more. Bungie announced on its website the first details on this year's The Dawning event, which will see Destiny 2's social spaces, the Tower and Farm, decorated with a festive look. Additionally, snow has fallen and you can take part in the merriment by partaking in snowball fights with other players.

This extends beyond the Tower and the Farm, as you can now throw snowballs at enemies in Strikes to stun and damage them. Also new for The Dawning is the return of the Crucible's Mayhem mode, which is not holiday-themed but who cares. Additionally, there are new Dawning engrams that you can earn each week by completing milestones in Crucible and Strikes.