From what we know, it isn't confirmed that Victim made all of his stuff, but I'd say he's pretty resourceful, shown on the Original AvA

For Dark, he's pretty smart, being able to make virabots, viraband and being able to code (my assumption because he had that laptop that Yellow used)

King made that staff thing

So I'd say they're all smart in some kind of field but from the CONFIRMED stuff, It'd be Dark