Trouble with Thanatos.

I'm having trouble defeating Thanatos. Now before anyone asks, my party is around LV 50; some are a bit under, some are a bit over. Anyway, losing Rayanne was a real kick in the pants, as she was my mage and partial healer. Without her, defeating Thantaos is difficult. Despite that, I know I could do it...if it weren't for the fact that he keeps paralyzing my whole party, and I've only been able to find one ring that protects against that ailment. So, what's a good way to beat Thanatos?