I just have to ask again, was the song "Sing Gloria" used in the game? It's one of my favorite songs from the soundtrack, but I don't recall hearing it while playing GunGirl 2.

The song is not used in the game. Josh made it as a special bonus track

I see, so my memory is not quite as bad as I thought. I think it would have worked well as a credits song, but Libera Me is also great of course

Interestingly, Sing Gloria's vocals are the basis for many of the demonic voices and utterances that you hear in the game. So one might argue that it is, in fact, in the game (;

Also, Sing Gloria is entirely based on "Gloria Fatalis" which is a boss tune.