I don't even need to do it for 100% or platinum (past finishing one fiend tale), but i've spent literally HOURS on Creature Creator in FFX-2. I don't recommend it, since you don't control fiends and literally just watch them fight for that long. I've grinded to 99 in KHRe:CoM, i've 100% KHBBSFM, I've platinum'd FFX HD, Creature Creator is just the worst o.=.o