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