does anyone know how to get the last hidden achievement I finish the other two, finale of corruption and finale of temptation.
Complete Lukka's research on your symbiote, make Torgar to reject corruption, make an oath to Drenth (the dragonborn in the castle in Nyx realm). Then when you acquire the medallion of the void, tell their names to it (it should glow with a bluish white colour) and defeat Nyx boss. There will be unique option after it, take it.