Ive been thinking of what Darkness 4-5 is going to give. Not sure if the quests give any hints to what it gives but it might either be a sensing buff or maybe an insanity based item that can buff you depending on your insanity level. Similar to the diamond item that sentinel has. Or third option, its just going to give an exploration buff for dark sea or something related to dragons. Lowkey want a pet dragon to fly around on. 
Maybe an oath diamond-like item that buffs you depending on how much insanity you have? Oh, wait, thats literally what you said, I need to read properly…
Then, maybe a ghost summon tool? Bootleg “summon elemental“?
Oh that actually sounds sick. I’ve always liked NPCs helping you fight, it was really funny getting my crew to help me fight stuff. The summon ghosts could be powerful because I saw some ghosts in far reaches that are probably lvl 600 because they have the same aura size (in sensing) as the nightmarish atlanteans 