A Cwn Annwn is a race in the Chronicles of Nick book series.
A Cwn Annwn is a spectral hound from Welsh mythology and folklore. They are messengers of the gods and guarded the gates of Annwn. They were sent to hunt down the dark ones and Children of Llyr, and unchristened souls. The gods would use them in battle and it was said that anyone who heard their baying would die. In this way they are like a Banshee.
Kaziel is a Cwn Annwn.