Having been to the Worldwide Invitational, we were hot to turn in our key that gave us a pet Tyrael. Running hither and yon in the Undercity, we finally found the NPC for the turn in, said the magic words and voila! A floating, lightning-winged avenging angel was ours for everyone to ooh and aah over.
Well, kinda. It doesn't really do anything. There are no animations other than floating. Don't believe us? Check out the video above. At least Sleepy Willy had the good manners to fall asleep occasionally.
EDIT: Apparently he will dance with you if you target him and use the /dance emote.