Lol, I actually found out how to kill this by accident and help, someone told me to eat the thing and then I started shooting the Golem, at a time I missed the Golem and the golem changed colour, so i started shooting like mad, not short after he returned to normal, as for dumb luck it happened again, at that time I saw the other creature on the floor as I figured I had to hit that, which somehow got very hard all of a sudden.
It seems like I got more luck then skills. >_<
Also that when it became near death, I ate a few things and I got invincible, while I did not eat the Legendary cake. I guess I ate so many diffferent defence foods that I got so tough it wouldn't hurt me at all, or so little that I couldn't see my life go away.