Def Jam Rapstar

This is one of the most difficult trophies in the game to get since it is basically the culmination of the entire Career Mode. The nice thing is that you can play on Easy for all of the songs, although I'd recommend trying them on Hard first so you can get enough performances for the 'Unstoppable' trophy. Basically, you need to get an “Off The Chain” (5-Mic) Performance on every single song and challenge in all 5 Stages of the Game. This is essentially 61, 5-Mic Performances (45 Songs and 16 Challenges).

Tips for 305 Mics:
Practice. Seriously. The only ones that really gave me trouble were Salt-N-Pepa's "Push It" and the 75 word in a row challenges (Twista, Children's Story). With "Push It", some of the timing with the "Ah, Push It" parts is a little screwy and the song doesn't have that many lyrics in general, which gives little room for error. With the "Ah, Push It" parts, just say it in a louder tone, rather than the almost whispering tone they do in the actual song. It simply takes practice and you'll eventually get it. With the 75-word challenges, this takes a lot of practice and a bit of luck as well. The Twista one can be intimidating, but just practice it enough for the timing and you can mumble a lot of your way through it if you can't keep up with all the words. Just make sure your mumbling is fast enough that it still registers on one of the gold circles. The nice thing about these challenges is that the lyrics and pitch do not matter, it's all about getting the gold circles by any means necessary.