The Winter Holiday DLC, or rather event, was activated around Christmas and was only available on holidays. This happened in 2016 and 2017.
The following content came with that event:
– A new free mission is added to the game. Help Santa to rescue his reindeer and save Christmas for people all around the world!
– We’ve changed our main menu art, so it would be more suitable for this time of year;
– Redesigned the UI to give some additional holiday vibes to players;
– Added some holiday trees to the map generator, brings even more joy to the game!
– Peasants now use their holiday colored bags;
– Tweaked the lightning for a snowier atmosphere in the game.