Didn't bother getting KotR against the weapons even the first time I fought them. I can't remember if I used Bahamut Zero or the Gil-tossing against Ruby. Probably the gil-tossing, since Bahamut Zero's animation is so darn long and gets very boring after a while. It did take much longer, but I also felt a great satisfaction from being a hipster like that.

I remember doing some challenges vs Ruby and Emerald later on too, but my number one biggest achievement would probably be completing my whole "lowest possible level, initial equipment, no materia" challenge. The final boss battle during that challenge was pretty darn intense.