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