The Surefire Way

The High Elves are erecting a siege camp, and you wish me to send my Dragon to raze it? The power of a Dragon is rarely bought so cheaply, but I have grown fond of this sword. I will help you, but only because your plan furthers the aims of the Witch King. Take this Horn. Using it within sight of the camp will summon my magnificent pet to your location. Get as close to the camp as possible before using the Horn, for Torthirog will not bother to come if he can't smell the flesh of the kin-traitors. Once you have called him, you must beware of his fury, for in his wrath he will not distinguish between you and our feeble cousins.

Travel to the High Elf siege camp, north of the Steelwind Manor. When you are within an adequate distance, use Iorikith's Horn to summon Torthirog, the Black Dragon. Return to Kronathi the Viper in Honor's Scourge when successful.