Campaign:
Hard achievement. I had a hard time, until I found a good strategy. First stone: Just go a little tiny bit on the right side. Just very, very little. Press "A" and don't drag. Power: Full! With this shot, you should hit the yellow on the left side. (The one who is the farest from the middle) For your 2nd stone the 2 yellow stones left, have to be near each other. Another straight arrow, that will hit both stones. (Use map on the top left for better view) You will know what I mean. No dragging and full power. Ah yes, and always mop. On both shots.
Achievement unlocked!