The event starts Tuesday (12/22) and ends next Monday (12/28).
Rewards
The main rewards this month are a Rune of Gold, Book of Spells, Rune of Builder Elixir and a Shovel of Obstacles.
If you are only interested in Gems, you can get up to 300 Gems by selling the items.
Bonus Reward Point Threshold
Introduced on the Halloween 2019 update, you can pick an extra reward from any unlocked tier if you individually reach 4.000 points (max points possible).
Unlocking the Last Tier
To unlock the last tier the Clan must achieve 50.000 points. With the limit of 4.000 points to each member, the clan must have at least 13 active members to unlock the last tier.