Free idea, maybe stupid: An advent calendar that is also a board game playable from day one. You start with something very simple (puzzle game or racing game), but as the days progress, you get more pieces and rules, so the game mutates and gets harder. By the last day, you have a challenging board game that the whole group/family already learned how to play.

And then someone will be like "I enjoyed the game from day 17 a lot more" and that's fine. It's your game, you can do whatever you want.