There is a paper on the dining table that shows the order of which you need to ring the bells that are in the lower rack of the kitchen top, if done correctly you'll trigger the Christmas event. Besides the scenery changing, you get two extra tasks to complete: Decorating the Christmas tree as well as building a Ginger Bread House.

Could we get a Christmas% as well as an AllEvent% or something alike? One for just the Christmas events and one for the whole game plus the christmas events.

A Christmas% would be cool.

As for AllEvent%, these questions would have to be answered first:

Does the Halloween event trigger tasks?

Are there other events?

Will either of the above answers change as the game updates?

To my knowledge there aren't any Halloween tasks, but as a mobile player I'm not sure whether it has changed with the newer update.