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