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