Realistically, mercy wouldn't work on GV1/2 bosses. GV1 bosses would just call GV a retard and continue to go after him or the people he loves since they're scumbags. GV2 bosses are too fanatical to take a second chance. To be frank, I'm surprised that it worked with ATEMS at all, as they seem to worship ZED more than Eden worships Zonda. ZED seems even more convinced of his path than Nova (not sure about Zonda, depends if she was killing all minos because of raw hate or saw it as a necessary evil to save adepts). The only game where it would work would be iX. Most of iX's bosses don't want to fight Copen, and it'd be easy to convince them to fake their deaths so their loved ones don't suffer reprisal after Copen beats them up, but mercy isn't a word in Copen's vocabulary, so...