Brettspiel Adventskalender 2017Expansion

From BoardGameGeek:

Brettspiel Adventskalender 2017 is pretty much what the name says it is: A board game advent calendar for 2017 that contains 25 small expansions or accessories for 25 different games from different publishers. The game rules for each item are included, but they will also be posted separately on the publisher's website on each day from December 1st to 24th. There is also a bonus 25th small expansion behind a secret door.