Snowflakes are materials that can be used to craft the first craftable Dragonforged Armor, the Hyaline Sleetrobes. You need 600 pieces to craft the armor, and once you reach level 35, you need 600 more pieces to craft the plus version (1200 total). The event ends at the end of the day on January 3rd, 2016. Best place to get snowflakes is on the epic stage on Haunted Citadel or Kingdom of Darkness.
Gulfguard Marker Step Chest, Terrestrial Bulwark Chest, Fusion Tree Bling Chest, Limited Edition Shadowflame Ember Chest, Limited Edition Sentinel Mark Chest, Limited Edition Heroic Loot Chest (plus the normal chests including the Bossarmor Chest).