Guitar Hero: Warriors of Rock

In Quickplay+, you can earn up to 42 stars on one song. There are challenges for each instrument, and for the full band, for each song. You can get up to 36 stars from these challenges, 3 for each one. You can also get 5 stars for getting a high score, plus one more for hitting 100% of the notes in one streak (also known as a Full Combo, or FC).

For each song, there is also what's called the Power Challenge. In the Power Challenge, you combine two of the character powers you've unlocked in Quest mode for a really high score. My personal recommendation is Star Power Generator+ (Echo's power) and Star Power Nova+ (Pandora's power). You can earn up to 21 stars in a power challenge, which also count toward the 500.

Most people play guitar/bass, so if you do only the guitar and bass challenges for one song, you could get up to 15 stars for the challenges, plus 6 more for an FC. You could also get up to 21 stars in the Power Challenge, for a total of 42 stars on guitar/bass alone. Of course, not every song is the same, so if we approximate 40 stars per song on guitar/bass alone, it should take around 13-14 songs to reach the 500 if you only play that instrument.

This achievement is unlocked by obtaining 500 stars in Quickplay.

You earn stars by completing songs, as well as completing set challenges for each song. Each song can earn up to 42 stars if you use all 4 instruments (Drums, Guitar, Bass, Vocals), but can net you at least 14 with one instrument.

Each challenge is worth 3 extra stars, and there are 3 challenges for each instrument. Add to that the 6 stars you can earn by achieving 100% on the song.