The mythical relic Dirge of Arkovia (Vitality Damage pet Relic with + to all skills in Necro) currently builds from the relic Vendetta (Pierce and Elemental Damage with + to all skills in Inquisitor).
I believe the intended upgrade path after the latest patch is Mortality (Vitality Damage pet Relic with + all skills in Necro) → Dirge of Arkovia
After a quick check I didn’t find any other tread mentioning this, so I’m unsure if it is known or not.