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