When you face Rokara as an enemy in Mercenaries (PvE), it often shows up in the “Deafiant Rokara” Skin – a heroportrait which was obtainable in the shop several months ago and was desinged only for the traditional Hearthstone modes (standard, wild & timeless).
You can’t acquire this skin in the mercenaries mode and I’m pretty sure that all the skins from actual existing mercenaries you face as enemies in PvE are also intended to be obtainable. Maybe the code for this Rokara skin slipped somehow into the mercenaries mode, but I think it’s not meant to appear there.
Thanks for referring to the original discussion.