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