This is obviously a mistake.
so its just a achievement with nothing spec u get from it, na im good waste of time
Most probable thing: Somebody messed up. Because let's face it, Rygelon doesn't have any real connections anywhere, so why should he be something unique for the Prepatch? It's the same achievement as it is available now already, just for the other difficulties. Which honestly is already quite the annoying thought with the forced movement on a boss that forces you to have fairly precise positions for soaking the orbs in both phases.
Hm, does this require specifically Fated Heroic/Mythic, or can it be done on regular Heroic/Mythic?
No points, no reward, nothing… that annoying achievement on hc/mythic would deserve a cool title/mount or both🤷♂️🙉