Darvin: Anyways, your best course of action is to nuke this thing with alchemist fire or holy water. Buy a big stack of these items and just barrage the mummy with them. Its damage reduction doesn't apply to elemental damage, so even though these items are low damage they'll whittle it down very quickly.
Small problem: those items were only added in the expansion. No luck in the OC.
To the OP:
Two easy options present themselves.
1] Go somewhere else. Do other quests. Come back at higher level with stronger weapons. Make sure to keep any +2 weapons you find. (Missile weapons included. You don't need a +2 enchantment bonus: +2 attack will be quite enough. But note that +2 arrows or bolts won't help. You need a +2 bow. +2 darts do work.)
2] Get a strong henchman. Daelan should be able to hurt the beast. Certainly if you level him up far enough: you can easily go above level 10 in chapter 2, and at that stage henchmen should have +2 weapons.
Not as good, but still possible:
3] Use a weapon that deals elemental damage. Fire damage, preferably, since most mummies are vulnerable to it.
4] Set traps. Fire traps, preferably. Will work a charm, but you may not have the skill.
5] Use spell-scrolls as the Hilltop suggested. Again, fire helps. Or healing! Healing spells hurt the undead. However, you need the Use Magic Device skill.
Oh, and if you happen to be a cleric or paladin or Bard, you can just cast Greater Magic Weapon. If you're high enough level. But of course, those characters aren't likely to struggle against a mummy lord anyway, and have lots of other ways to kill it. (Though a bard might have a harder time if you don't use that spell.)
