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