So I'm completely ignoring the old man's warning in the Lunar Ruins and trying to kill one of the damn things. I'm currently using Rydia (Mist Ring for added evade boost with Mist summon), Cecil (no Lightbringer), Porom (Nirvana + secondary healer), Rosa (Primary healer), and Yang (using Hand of the Gods, Dragon Claw, and Discipline Ring). He's killing me really quickly. Should I finish all of the other character's trials, or just switch out my party?

I also screwed up Rosa's trial and want to know if I can do it again. Or if the reward for doing it is even worth it.