Guitar Hero: Metallica
51 Achievements
112-136h
PS3
Robert Trujillo
Complete the career as the bassist
5.8%
How to unlock the Robert Trujillo achievement in Guitar Hero: Metallica - Definitive Guide
Like others have stated that it can be done on any difficulty. You'll need to get 72 stars to unlock the Ice Cave. Once you do that, play the song "The Thing That Should Not Be" and the achievement will pop up as soon as you beat the song.
Only remember you have to play solo career. In band career doesn't unlock.
All you need to do is go on any difficulty (I recommend easy as that will get more stars) and play the easiest songs until "The Thing That Should Not Be" unlocks, play that and you will get the achievement
This is very straightfoward. Just beat the career mode as the bassist. It could be done on any difficulty so stick to one you are comfortable playing on.
Beat the game on the bass career by beating "The Thing That Should Not Be" after getting 70 or so stars. Difficulty doesn't matter either.
Connect your guitar hero guitar to your ps3. Using the guitar to navigate, select "career" from the main menu, then select "bass". Then, select the difficulty you are comfortable with.
It is not necessary that you complete all the songs. The way the system works is that once you have earned a specific number of stars (depending on your performance in each song) a new stage will unlock with a whole new set of songs. Once you reach the final set (which only has one song in it, complete the final song and you will have completed the career as the vocalist and will obtain this trophy.