Here is the full list of all 23 Mallow Drops achievements.
Died 20 Times
Completed World 5
Enter Sequence 5
Found the hidden item in World 5
Completed World 4
Killed an enemy with a laser
Enter Sequence 4
Found the hidden item in World 4
Completed World 3
Sent an enemy out of bounds
Enter Sequence 3
Found the hidden item in World 3
Completed World 2
Enter Sequence 2
Found the hidden item in World 2
Completed World 1
Rotated 50 Times
Enter Sequence 1
Finished a puzzle without rotating
Found the hidden item in World 1
Sent a block out of bounds
Finished a Puzzle without dying
Sent all blocks in a puzzle out of bounds