I beat the Necromancer last night. I finally realized that my berserker sucked and turned her into a warrior. Much better results, the hit percentage for the warrior's attacks were a good 20-30% higher than the Berserker with all the same equipment and skills. Also that...Trusty Shot (I think it's called?) ability that the archer gets that costs 40 TP is really useful if you need a guaranteed hit. I wore down the skeletons and phantoms with my front line fighters, built up Canpous's TP and sent him up- one finishing move and one regular attack on the Necromancer took him down.
I then did the next few story missions which all seem really easy now.
I then did the next few story missions which all seem really easy now.