I actually found a fire/earth mage to be just fine in the flaming-undead area for the simple reason that the fire elemental summon is invincible against Mr. Two-Head, which makes it an excellent blocker, both there and in the Braccus battle. The wolf summon is also a pretty strong attacker even without the AP reduction from rangerish stats. (I'm not sure if that's intentional - the spell requires earth magic 1 to learn but apparently falls under survival skills instead of earth magic?) Sure, he won't be doing very much damage personally, but between summoning and buffing (and by that point you have some really strong buffs), the F/E mage certainly isn't going to be left twiddling his thumbs there.
