I looted the Raid Finder version of Gurth'alak last night and have been doing some testing to see where it parses out to compared to the normal Sulfuras. I've heard really good things about the tentacle damage and the RF version out-performing Heroic 391 weapons, so I figured I would give it a shot.
I don't know if the tentacle is bugged, I can see the animation of the tentacle and I can see it channeling mind flay, but the event isn't appearing in my recount or my combat logs. Is anyone else having this issue with the proc off of Gurth'alak? I opened a ticket but the current wait time on my realm is over 4 days so I just wanted to see if anyone had any insight into what is going on with the proc off of this sword.