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