When Valhalla started out and we were given the first set of 3* and 4* heroes, two of the heroes, both Valkyries, somewhat mimicked the special skills of the elite enemies at the Midgard Valkyrie stages. (Mist being an obvious one since she was the boss in all of these.)
The nature Valkyries, the Valkyrie Defender, had a skill that had some similarity to Brynhild, gaining immunity to dispels and mana generation. But we currently don’t have an epic/4* dark Valkyrie that has a similar “stack” ability to the Valkyrie Ambassadors.
I propose a hero who deals slight damage to target and nearby enemies, like Mist. No debuffs or damage over turns, but the Dark Valkyrie Hero will perform a stack for attack and/or defense on themselves and short counterattack for caster and nearby allies. Not sure how to do the hero that would be like Brynhild and Mist but doesn’t make them too out there.