Recently I transferred my main to my secondary bnet while I shuffle characters around (I hit the 50 character limit on my main account). I discovered something interesting in the process. Part of the reason I moved my main was for the Insane title, I decided I wanted to offload my auction house activities to this account so why not give my bank characters the title they deserve in the process. Since the title is tied to reputations, I wasn't concerned and it DID indeed work. I found however that several other things that I wouldn't have expected to transfer came along as well.

First, multiple titles like Herald of the Titans came along too. That one was especially surprising as I didn't complete the Herald achievement on that character, but rather my Warlock. Additionally, numerous transmogs came along for the ride too. Notably the Challenge Mode transmogs and ones that are no longer available in game such as Halberd of Smiting which was originally dropped in ZG and was removed when the zone was updated.

Additionally, the class mounts from Legion are transferable, however you might have to talk to a GM to get them moved. And it will remove them from the bnet of origin. So, if you're looking to consolidate characters or maybe just wanting to ensure all 10 of your characters have certain mogs available this could be some useful information. If there's any interest, I'll compile a list of all everything I can verify that came transferred over.