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