This one is simple enough to get and doesn’t require too much skill. First of all select a song you wish to play (I suggest “2112 pt.5 – Oracle: The Dream” by Rush as it is the shortest on disc song and fairly easy) and when it brings up the options for the song on the right select Star Challenges. This brings up the challenge menu for that song, scroll down to a challenge for your instrument (make sure to select high score) and press blue before selecting it (this changes the leader board to overall). It will then take you to the little leader board in the middle, scroll all the way down to the bottom as this is the worst song on the leader board (therefore easiest to beat) and select. Now all you have to do is beat that grade (not score, so if the current grade is gold you need to get platinum or diamond), this shouldn’t be hard as the chances are this person had a very bad run on the song. Once you have beaten the set grade the achievement is yours.