Originally posted by Kursor1:

I will note that it appears to be tied to mounting the trophies on the starting stones. On The_Emily_Show's community server we had a guy do a bonemass challenge on a different server to avoid triggering bonemass stuff on the comm server, but mounting the trophy on the comm server triggered the progression anyway.

Hanging heads not trigger raids in random worlds, the time that the boss is first dead in that world do