how do you dealing with black dragons as a mage ?

[Gatts]

Fighting black dragon with another dragon (red/black) is not as useful IMHO (Emerald one is OK - he is dealing PHYSICAL damage)

Against black/red dragons? -> Archdemons 85% Fire resistance, what is handy against fire attacks for these nasty dragons, teleport (can flee in the most away corner, or attack the best hidden enemy) Each start in the round they dispell all negaive spells, but still can bear positive spells... AND there is nice mod that makes them even more HANDY.

On maxed level sacrifice works for archdemons (not to mention you can have demons in your army, one of best middle level TANKs if not best, who can summon demonic army, good source of sacrifice)...