Here is the full list of all 18 Picrastination achievements.
Complete all levels in the Halloween level pack
Complete all levels in the "A Is For Anthrax" level pack
Complete 111 small levels in endless mode
Complete 5 Daily Llama puzzles in the Daily Challenge mode
Unlock all colour schemes
Score 100 points or more in the Snake bonus game
Complete all Huge puzzles
Beat the par time on every level to collect all the Par Stars
Unlock all audio themes
Complete all Large puzzles
Complete all Medium puzzles
Complete a Mosaic level
Complete all Small puzzles
Beat 20 levels in Endurance mode
Beat 10 levels in Endurance Mode
Complete all Tiny puzzles
Beat the par time on the groundhog level
Complete a puzzle with one mouse click