From PokéHeroes Wiki
Advent Calendar Event
To make the wait for Christmas a little more bearable, we are having our traditional Advent Calendar Event! Behind each door of our calendar, an individual task and a small reward are waiting for you: Maybe you get an evolutionary stone, maybe just a berry - or maybe even an exciting new Event Egg! Anything can happen.
This year you can pick from five different advent calendar designs; they are the winning entries from our recent community drawing contest!