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