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