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
Merry Christmas Puzzle Complete!
Cookies Puzzle Complete!
Nativity Puzzle Complete!
Presents Puzzle Complete!
Father Christmas Puzzle Complete!
Bear Puzzle Complete!
Cake Puzzle Complete!
Socks Puzzle Complete!
Cat Puzzle Complete!
Popcorn Puzzle Complete!
Apples Puzzle Complete!
Friends Puzzle Complete!
Gift Puzzle Complete!
Gnome Puzzle Complete!
Santa Puzzle Complete!
Teddy Puzzle Complete!
Taken Puzzle Complete!
Nut Cracker Puzzle Complete!
Snowman Puzzle Complete!
Toy Santa Puzzle Complete!
Mince Pies Puzzle Complete!
Complete Santa Hat
Baubles Puzzle Complete!
Bells Puzzle Complete!
Dawn Puzzle Complete!
Bridge Puzzle Complete!