my party is Random (54), Luciana (50), Sparky (44), and Sarah (49).<--all from the result of getting lost in the Witch Wood. unequip them from any counter-hit/spell (because that green spirit will keep fighting back until you die). buy shark meat from the Rilla Port which could give you 250 hp apiece (you don't really need it but this is just in case).
start your battle by castng the group spell to get rid of the skeletons and weaken the spirit by using Sarah's Soil Typhoon (that thing's vulunable to shrink). heal your party as soon as hp bar is about or lower than half. if you have it, cast ? (i forgot the name of the spell that Luciana has when Sparky is in the party) that costs about 44mp per turn. cure mad as soon as the character's inflicted (i used cure-all item i got from fighting/searching)