I stunned a sentry (forget which name) in Shadeweaver's Thicket and Groo's name popped up in Extended Target list. When I stunned the sentry again, he disappears until the sentry starts fighting again. The sentry was far aways from where Groo resides. Blurred the sentry and Groo was no longer threatening and back to indifferent.
Groo can be stunned but not mesmerized. I have a glowing drum which is as fast as knight's horses and he kept up with me, even catching up when he tried to cast a spell. I killed him and he has no faction tied to him.
Edited, Feb 3rd 2012 8:57am by Byren