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