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