First of all, you WILL NEED Gain Hypers, like 9 or at least 8. Secondly, do not attempt this until you are at lv.41. Which is the level you're probably at after fighting Ninetails, give or take.
Why? I don't know, but I do know that it's the first level where Marino reaches a speed higher than 67 (which is 68), making Quicksilver >200. You could try this at a lower level, but good luck.
For the same reason, it's recommend you equip the Turbo Buster and the Gurenken (Red Lotus Saber) for X and Zero, in order to not limit their speeds.
Marino is equipped w/ Fire Comet (not Stella unless if you use Hawkeye), I also recommend her to equip Chou FM alpha, though not needed..
Although I said no Build Speeds are required, you might still want to use some, it's just however many you've accumulated on X & Zero throughout your play through. Again, just to be safe.
I never needed to do this, but if thou must, you may equip Chou FM Beta, Speed+10/5/3/1 FMs, Boost Speed. Note: Boost items do NOT work in Hyper Mode, and they are negated once Hyper Mode is entered as well.
Start the battle with X, Zero, and NOT Marino.
The battle starts (I always do this at the Factory, not the Mine):
If you see a Preon Tank, do what you want with it. Ignore/destroy, it's your choice. I would personally destroy it because it's an eyesore. :P
The battle starts:
Take it easy, defend and build up WE until it's 100 (especially Zero). Then wait until you see that each of your character has 2 turns in a row before the Glob. This shouldn't take long.
On your first turn w/ Zero, swap for Marino, go into HM, and spam your Fire Comet for 25/26 turns, X's turn should come up in the middle of this, when he does, use Ultimate Armor and DEFEND.
25 turns: >6 million exp 26 turns: >9 million exp
You could go higher, just make sure not to overflow your system's number counter like I did once.
How to count: Once you activate Quicksilver, use Gain Hyper once you're down to 1 turn left. That should be 4 turns (assuming no Build Hypers are used on her). Then it's just keep on adding 3 between each Gain Hyper usage. To be safe, once you think you've accumulated enough, keep draining Quicksilver Gain Hypers and Fire Glob's LE with Mirage Dive, for safety reasons.
Once Marino cools down, swap back Zero, Absolute Zero, Calamity Arts, and finish it! (You WILL most likely need Ultimate Armor's Nova Strike as well).
NOTE: If your exp ends up being less than 4 or 6 million, I recommend you soft reset and do this again. Those Gain Hyper's sacrifice should come in big returns.
It takes about a half hour more or less to become from 41 to 99. :D Happy gaming!
What's the difference between the original and the localized version? Original usually means JP version and localized usually means North American/US version.