This special event happens every year from: 1st December - 6th February
Although not being those dates above in in between, it was released today/there 13/11/2018 because it is currently the only event known to be discovered in the code. There is a possibility there will be Christmas & Easter event but will not be put on this page link. The Halloween event has happen except this was replaced with the demo of "Freezing Pluto". The next halloween may have a proper Halloween event than a demo release playable without hacking the game.