I was playing around with a downloaded archmage savefile and wanted to test some stuff. I entered the chaos plane for a ULE and brought Andor down to critical. After slaughtering white unicorns, farmers, and children, I was C-. The GB states that finishing him here should give you an UCG.
But, I switched to Sceptre to finish him off, and I got.... an OCG.
I hope this isn't common knowledge, cause I spent a while getting the sceptre. But since the regular OCG doesn't need sceptre to kill him, it is odd that I would get an OCG in this situation.