I’ve done this fight a BUNCH of times over the past 3 days or so, because you can get Mana Crystals from it, and also because Amodar was being nasty and refusing to drop his monster crystal. And I noticed something very strange. At first, I was always killing Amodar first and saving Lightning for last. It seemed the logical thing to do, since Amodar’s far more annoying than Lightning is. So I did this fight at least 50 times, saving Lightning for last each time. In the process, I had Lightning’s monster crystal within the first half-dozen battles or so, and (with the help of a Durable Collector’s Catalog) I was seeing her rare drop roughly every 3 fights. (I had 15-20 extras to sell at the end.) Yet over the course of the same 50 fights, I never once saw Amodar’s crystal, or his rare drop.
Suspicious, I decided to change things up and kill off Lightning first for a while. And lo and behold, just 5 fights later, I had Amodar’s crystal and I’d seen his rare drop twice. And at the same time, I suddenly STOPPED seeing Lightning's rare drop.
Statistically speaking, that should be nigh impossible, leading me to this little theory: The order you kill them in matters. For some reason – either a glitch or deliberate design – the enemy defeated first in the Lightning/Amodar fight has ZERO (or at least an exponentially smaller) chance of giving up their monster crystal or their rare drop. (But why this would not extend to common drops is beyond me.)
I suppose it is possible – though highly unlikely – that my PS3’s RNG was just being really, really weird over the past few days. But given my experience, my little theory strikes me as far more likely, yet I've never seen anything here on GameFAQs to that effect. If this phenomenon has been noted before, I was hoping for some corroborating evidence. And if there are others out there having a freakishly hard time getting Amodar’s crystal, it may well be because of this.
"Personally, it's not God I dislike. It's His fan club I can't stand." ~~bash.org