People keep saying how hard this is, I got it quite easily on my first try.
Party Members: Not Optional
Suggested Level: 35 - 37
Equipment: Strongest weapon and armor, any anti-freezing skills, MP replenishing skills
Now, as you may know, this boss reflects ALL magic back at you, so don't even try. This means physical attacks are your only option, obviously Mack will be doing all the damage dealing.
When the battle starts, have someone cast the strongest form of Powerus you have on Mack, All-Shield and All-Barricade on the party, Any speed up move can help too. Mack should just use 'Combo', this should, if you're at the suggested level, between 1200-1500 total damage.
The IMB usually attacks in a pattern, so you can easily predict what move will come next after a few cycles. Be sure to heal as much as possible before it uses Absolute Zero, this will almost always freeze someone if you don't have anti-freezing equipment, freezing usually wears off in a few turns. It's also wise to have Ming and Cooke alternating Zephyra, or at least Zephyr.
I only had to revive Ming and Cooke once each, it's a pretty straightforward and simple fight.