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