Here is the full list of all 30 Pepper's Puzzles achievements.
You completed everything! Congratulations!
Complete the trial "Marathon" with 3 stars
Complete the Mosaic puzzle "The Apprentice"
Upload your first puzzle to the Workshop
Complete the Mosaic puzzle "Moonlight Warrior"
Complete all classic puzzles with 3 stars
Complete the Classic category "Run out of Ideas"
Complete the Classic category "Extinct Animals"
Complete the Classic category "Apocalypse"
Complete the Classic category "Space"
Complete the Classic category "Movies"
Complete the Classic category "People"
Complete the Classic category "Daily Routine"
Complete the trial "Meek VS Giant" with 3 stars
Complete the Classic category "Sci-Fi"
Complete the Classic category "Art"
Complete the Classic category "Videogames"
Complete the Classic category "Animals"
Complete the Classic category "Food"
Complete the Classic category "Fantasy"
Complete the trial "Climb" with 3 stars
Complete the Classic category "Life in the Farm"
Complete half the cells of a Mosaic puzzle
Complete the Classic category "Warm up #2"
Complete the trial "10x10" with 3 stars
Complete the Classic category "Warm up"
Complete the trial "7x7" with 3 stars
Complete the trial "5x5" with 3 stars
Complete your first cell in a Mosaic puzzle
Complete a classic puzzle with 3 stars