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