For those who'd like a little perspective on how difficult it is to really get this thing, I decided to go ahead and crunch some numbers. Using the helpful Hidden System Sector FAQ, I took the SP multipliers in the sector and figured how much you could potentially win just by betting 50% on every challenge and winning.
Bad news? Beating all 13 challenges with 50% of your SP at stake each time, by itself, will net you just shy of 1.3 million, falling short of the necessary 1.5 mil.
Good news? That's just factoring the multiplier and the initial 1000 SP they give you at the start. Factors like SP gained/lost in the sector itself and 'virus' floors were not considered.
So, for those struggling, here's the protip: do as much as you can while in the sectors. Fighting heartless, busting open prize blox, and not getting hit will help give you the extra SP you need to bump you over 1.5 mil. However, prioritize clearing the mission, and be sure to go 50% on EVERY challenge to stand any real chance of getting it.
Me, I've still got some levelling to do before I try again (killed on the 12th floor, of all things...), so good luck to y'all!
"Lesson Lesson: If you see a stranger, follow him." -Ed, Cowboy Bebop
My first time through I was getting a lot of the golden fungus. So by my 11th floor I was well over the 1500000 SP mark. I thought that I could leave the sector and get it for sure rather then take a risk with 100% bet. I found out it only becomes available after you beat all 13 floors. :(
Amy Anderson/Ami Mizuno lover! ^_^ Check profile for FCs.
My first time through, I actually got a virus floor on the second-to-last floor, though I kept dying at buggy Roxas, so I couldn't get Ultima Weapon. Though really, the last challenge is easy if you have Megalixirs equipped at the start of the fight. Just use one, use your finisher (Megalixirs immediately raise your clock level to its highest point) and clear the challenge.
After that, I just resorted to Dodge Rolling like crazy, occasionally throwing a Judgment Triad when an opening presented itself. Yes, it's pretty much cheesing him, but trying to attack him head-on is an exercise in stupidity.