I'd put a tiny advent calendar behind every door of the advent calendar.

Even behind the tiny doors?

It would need to be a little longer than your average advent calendar...to make sure it lasts through Boxing Day!

I would put another door behind each door, and behind each second door would be a puzzle piece

Of course, I would leave out the 26th piece with the best part of the puzzle on it

Man all of these ideas sound so cool.

My advent calendar just contains the blood of my enemies.