To get this achievement you have to warrior up all 8 characters then proceed to the last unlocked chapter. This can part of the game can be quite tough but not if you play it smart. Before you play any songs in this gig you have to choose 2 bands made of 4 characters from the 8. Choose carefully so the powers can be at their most effective. The thing that makes this gig difficult is that not only do you have to pass the songs, but you also have to get 12 stars before the end to use the power of the Legendary Guitar. Both songs to be played are by Megadeth, the first band has to play “Holy Wars... The Punishment Due” and the second has to defeat “This Day We Fight!” I suggest trying to even out your powers as much as possible to make both songs a relatively easy task.