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