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