Quote Originally Posted by Vivi22
Rhinox actually (like the Beast Wars character). I've never used that one before, but since other rages don't use Gau's MP to cast spells, wouldn't you just end up with the same "not enough MP" message the monster gets, or will the spell actually work for Gau? I suppose the easiest way to find out is to try.
It works. They can't cast it because they lack MP. Since Gau doesn't waste any MP when casting spells during a rage, he CAN cast it.

I don't think I used it during the first part of the sky battle, but if I remember correctly, I did use it during the battle after Ultros. I think the Rhinox absorbs thunder-based attacks. And if i remember correctly, that boss use a lot of thunder-based attacks. So by having Gau in Rhinox-rage, he become pretty much unbeatable as he absorbed most of the attacks and constantly casted Life 3 on himself.