Bah, I can't beat Suwako.
Thanks to Komachi I can Poison and Paraylze her while decreasing her Mind and Speed, but she still manages to own me.
Suwako I found easy (I ran into her without expecting it at all and tore her apart my first try), so I'm still not sure why people have trouble, but here.
She follows a pretty strict pattern.
She starts out in "Physical" mode. Her Physical defense is twice as high as her magical defense during this phase, and she uses single-target attacks during this phase. The fifth attack in this phase is Croaking Frog Eaten By Snake, used on the frontmost character.
After, her next turn will put her in "Magical" mode, where her defenses flip. She now uses multi-target magic spells for four turns, then finishes off with a final casting of Mishaguji-Sama on the fifth. Rinse and repeat.
Knowing this should help.