As always, spell drops are random. I've gotten drops off of most mobs, some more than others. This mob dropped the 54 Enchanter spell Dementia on my first kill of it.
You will see many more of these mobs in the northern portion of the zone.
They are as common as the regular Chromodracs if you hunt near the northern end of the zone - they congregate around the VP area I think. I wasn't brave enough to try one since I could barely tank the regular chromodracs.