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