Ten times normal, unless I miss my guess. It seemed about that way, at least. I took down Kid first, and considering she had something in the area of about 750 health normally, and I struck her with Forever Zero, Feral Cats, and about 40 or 50 strikes of 100hp damage, that amounts to about right. It was really easy, though, seeing that, not only was I at level 99, but also had taken away all elements, armour, and weaponry save for the basics from everyone (I wasn't sure what translated over to Lynx when you become him, after all, so decided to play it safe.)
Too bad it doesn't give a special ending or anything, though. After all, you cannot get it until at least the second time through; that would qualify it for special ending status, not unlike that in CT when you defeat Lavos at the Ocean Palace. I find it quite incongruous that Lynx falls down, even though, when I did it, he had about 750/850 health remaining: hardly enough to injury someone to near death.
