My friend and I just discovered an insane glitch in GHIII! I haven't searched the Internet, so this might be old news, but still:
We were in the Xbox Live mode doing Player Matches > Co-op. We were trying to 100% a song together for the "Legends...whatever it is" achievement. Frustrated at a particular part in the song, I exited out to the Practice mode, where I went over the troubling part a couple of times. Thinking I got it, we headed back to Live to Co-op it...
...and our song started at the exact point where I was having trouble! :shock:
It's crazy. We finished the song from that point, without missing a note, and I got my achievement!
He didn't though. I figured it was because I was hosting. We repeated the steps with him hosting, and it worked like a charm. He got his achievement next.
So we got to tinkering. Here's what we came up with:
Xbox Live > Player Match > Co-Op with a friend on your list.
Enter a song.
Play just a few seconds and then exit out.
Head back to the main menu, go to training, and select "Practice."
Play the last section of the song you chose.
Now, return to Xbox Live > Player Match > Co-Op and enter the song you just played in Practice mode.
You should start at the very end of the song...the spot you played in Practice mode!
This can help you get the 100% achievement!
(Only the one creating the match has to do these steps. The other person can just wait for the invite.)
What's more, if you then return to the Xbox Live > Player Match > Co-Op menu and do songs on Expert (we were doing 7 song sets), the game keeps putting you near the end of songs. In many cases, we would enter the song, only to see "You Rock!" The song would be cleared without us playing a note!
Some songs had us play portions at the end. Never really figured out why some songs did, and some didn't. Many of them we 5 starred, by basically doing nothing.
Sorry for the large post, but I am pretty excited at the moment. It was kinda funny and bizarre to find such a thing.
Note: Changing your character/difficulty/etc. should have no effect on the glitch. And if you are after that 100% achievement, it's only the person setting the game up that gets it.
I am going to bed now, but will post more tidbits if we figure them out later today.