Kronk has asked you to use the Banishing Crystal to banish 15 demons at Forge Camp: Wrath or Forge Camp: Terror atop the Blade's Edge Mountains. Return it to him once you have done so.
15x Demons banished
If we know the demons, and we do because we've studied them extensively, they're fast at work repairing any damage that has been done to their precious transporter.
So, if you want a chance at another darkrune, take our banishing crystal back out there and eliminate more demons. Besides, you want to help us to lessen the threat that the demons pose, yes?
We said "chance" because the process we use yields mixed results. You might get a darkrune, or you might get something else entirely.