It's a full song, quite lengthy (approx 6-7 minutes) with slow, heavy guitar-based riff (later on 'stolen' by Black Sabbath! ;-). Although some people still believe that it was originally a Wreckage song, in the early 90's Brian told me personally that it was written by him (music) and Freddie (words) in the early seventies. (So it is a matter of believing Brian's fading memory or not ;-)
It was played live on many early shows, never appeared on any album, but it is common believe that Queen did record a proper studio-version of the song, pressed on an acetate (test-pressing).
Unfortunately there is only one person that has ever heard this version. ;-)
Untill now it seems to be NOT in the official Queen archives and it does not look like it will get there soon. So basically we can all forget about ever hearing that studio-version...
(The day Hangman studio is in the archives, will be the day the Anthology boxsets go to print ;-)