[@Lightbox], that's actually what I was thinking about with Titan's Hand and Twin Wield which I brought up for discussion earlier.  They're hidden skills that you have to fulfill the conditions for before they even show up.  Still, that kind of skill would definitely need GM approval since they would all end up being effectively unique skills.  It's unlikely that two of the characters in this RP would end up fulfilling the same set of requirements for such a skill.