When you get an opportunity turn, it increases the stats.
Special Note: I'm playing on Hard!
I've beaten all the way up through the black king, and my party is level 30ish. The White King (last one) rocked me though. Granted, he's level 88, so it was to be expected.
Red King was easy as pie
Blue King I attacked with long range stuff, and kept them all apart so if he did get to use magic frenzy, it was only on one guy.
Green King basically tried to apply SE's the whole time, so easy.
Black King was a bit of a pain. But eventually I got him trapped between my Green Mage with dodge magic, and my Bangaa with the mirror armor. He couldn't hurt either of them. Only problem was he'd cast the spell on him and my Bangaa, and heal for 300 HP. Eventually my sage built up enough to use Ultima blow, combined with strong attacks from other characters before his turn came back, and I managed to kill him.
On another note, I adore the auctions. Just got some Ninja tabi, the book that teaches magic frenzy, and Ultima shot for my hunter(main character). So I'm pretty much rocking right now.
THE JACKAL