When you have the scales and the vial of blood in your inventory, you speak the spell and he loses his Dragon form. Now, you can defeat him in his human form. Even then, you want to be up close and personal with him because he has very powerful ranged attacks.


I'd like to close by quoting Bellegar's famous last rhyme:

"Cursed be the mother that bred thee!
The wench must have been a hell-spawned banshee!"