Here is the full list of all 15 Advent Calendar achievements.
Play the first minigame on December 1st
Play the final minigame on December 25th
Open 3 days on the calendar in a row
Open 10 days on the calendar in a row
Watch the fireplace for over 10 minutes
Listen to holiday music for over 5 minutes
Complete a jigsaw puzzle in under 1 minute
Complete a jigsaw puzzle of 600 pieces
Solve a jigsaw puzzle in multiplayer
Achieve 2048 points in a single player game of 2048
Achieve more than 1000 points in a line puzzle
Finish a pixel art picture in multiplayer
Complete a pixel art picture
Finish one day of Match 3 levels without failing once
Solve a sudoku puzzle in under 2,5 minute