Here is the full list of all 30 Depixtion: Halloween achievements.
Collect every Achievement
Play Depixtion: Halloween on October 31st
Play Depixtion: Halloween between 12am & 2am
Complete all 24x24 Puzzles without using "Show Mistakes"
Complete All Puzzles
Complete All Puzzles without using "Show Mistakes"
Complete all 24x24 Puzzles
Complete all 20x20 Puzzles
Complete all 20x20 Puzzles without using "Show Mistakes"
Complete all 16x16 Puzzles without using "Show Mistakes"
Complete all 16x16 Puzzles
Complete the “Nitemare” Puzzle without using X’s
Finish the “Mystery Solvers” puzzle in 30 minutes or less
Complete all 12x12 Puzzles
Complete all 12x12 Puzzles without using "Show Mistakes"
Complete the “Zombie Hand” puzzle using only the Mouse
Solve the 13th puzzle in less than 13 minutes
View the Advanced Tutorial
Solve a puzzle with Drag lock & Counting Disabled
Watch a replay 3 times
Quit the “Graveyard” puzzle without completing it
Wait on the Main Menu screen for 2 minutes
Finish the “Death” puzzle in less than 666 seconds
Visit the "Credits" screen
Solve the Blue layer first on any puzzle
Complete all 8x8 Puzzles
Complete all 8x8 Puzzles without using "Show Mistakes"
Complete all 4x4 Puzzles
Complete all 4x4 Puzzles without using "Show Mistakes"
Complete the Tutorial