Here is the full list of all 27 Pixel Puzzles 2: Christmas achievements. It takes around 4-5 hours to unlock all of the achievements on Windows.
Complete All Puzzles
Santa Puzzle Complete!
Nut Cracker Puzzle Complete!
Taken Puzzle Complete!
Cat Puzzle Complete!
Popcorn Puzzle Complete!
Gift Puzzle Complete!
Apples Puzzle Complete!
Friends Puzzle Complete!
Cake Puzzle Complete!
Father Christmas Puzzle Complete!
Nativity Puzzle Complete!
Cookies Puzzle Complete!
Merry Christmas Puzzle Complete!
Presents Puzzle Complete!
Bear Puzzle Complete!
Socks Puzzle Complete!
Snowman Puzzle Complete!
Toy Santa Puzzle Complete!
Teddy Puzzle Complete!
Mince Pies Puzzle Complete!
Dawn Puzzle Complete!
Baubles Puzzle Complete!
Bridge Puzzle Complete!
Bells Puzzle Complete!
Gnome Puzzle Complete!
Complete Santa Hat