Here is the full list of all 20 ZHED - there are Puzzle Game achievements.
Complete the Tutorial levels
Complete the first 25 levels
Complete 50 levels
Complete 70 levels
Complete the game
Complete the game without using hints
Complete 5 puzzles in a row without using hints and undos
Complete 20 puzzles in a row without using hints and undos
Complete 55 puzzles in a row without using hints and undos
Complete 85 puzzles in a row without using hints and undos
Complete the game without using hints and undos
Retry the same level 10 times
Use 30 undos
Use 5 hints
Complete a puzzle using only hints
Retry the same level 5 times
Use 15 hints
Use 30 hints
Use 5 undos
Use 15 undos