Conan is quite simply wrong here, even with respect to his own milieu.  The eponymous being in "The Devil in Iron" is completely immune to weapons except for one specific magical dagger.  Similarly, the baboon-demon in "The Phoenix on the Sword" is shown to be immune to a normal axe before Conan's specially enchanted blade slays it.  The line you quoted says more about Conan's boastful courage and bull-headedness than it does about the actual physical circumstances of the Hyborean world, or sword and sorcery in general.  I wouldn't worry that much about it.

Last edited by Blackadder23 (7/09/2014 1:51 pm)

There's nothing wrong with the idea.  It would be easy enough to implement:

1) Make corporeal creatures like undead and lycanthropes vulnerable to normal weapons.  Maybe you could destroy a wight, mummy, or werewolf simply by chopping it into small enough pieces.  Maybe a strong man could slay a demon with nothing more than cold steel (and even in AD&D, the weaker demon types are in fact vulnerable to normal weapons).

2) Don't use incorporeal monsters like wraiths or ghosts, or anything else that would be preposterous to injure with normal weapons.

3) Have fun!

Fire good!

(Also: I am the Angel of Darkness. The Hour of Redemption is at hand.)

"Of course you should fight fire with fire. You should fight everything with fire."
 
I was in the same boat as Yora in setting up encounters in my Hyborian Age campaign. My solution was to implement a damage reduction mechanic ala 3.x+ for creatures normally "invulnerable" to normal weapons.
I simply make the DR equal the HD. A gargoyle or succubus can still be chopped to pieces with enough force, or crushed by a giant-hurled boulder. Even bigtime monsters can maybe be hurt by massive damage from normal sources like ballistae, canons, giant-hurled boulders, and Conan.

Think of Beowulf ripping off Grendel's arm.