Abyssal Lich

A character that has already ascended to be a Lich can bring a Kulemak's Invitation to the Well of Souls and jump into the well. Doing so will take the player to The Black Cathedral; the end of the area contains a urn with the display "Embrace Abyssal Power?". Interacting with it allows the player to freely swap between the regular Lich ascendancy and the Abyssal Lich alternate ascendancy.