http://gw.gamewikis.org/wiki/Corrupted_Dragon_Scales
Since Corrupted Dragon Scales is classified as a spell, and not a monster skill, consider bringing Arcane Thievery when you are about to confront Kuunavang and see if you can steal this spell. =P
Arcane Thievery (and most likely, Arcane Larceny as well, since it's the same spell) can't steal monster only skills of any kind. Nor can Inspired Hex or Inspired Enchantment. (Inspired Hex + Crystal Haze vs Glint would have been fun though)