You unlock Diablo as a boss when we realize how to prove Lorath is Mephisto.
This is not a joke, in the prologue lorath’s shack houses a demonic skull similar to Diablo.
In Diablo immortal A demon named Skarn found out you can trap any demon from respawning by binding their power to one of their host skulls and drawing power from it.
By Diablo 4 I think mephisto has trapped Diablo and is siphoning his and Baal’s energy. I think this is due to Diablo’s black soul stone not being part of mephisto’s plan.
Diablo double crossed mephisto with the black soul stone move. I think in Diablo 4 mephisto has paid that betrayal back.
I’m fairly confident Lorath Nar is Mephisto in disguise. He lacks the character traits you’d expect from the real Lorath.
Lorath is also notably consumed by the demonic nightmares as Marius was before him and Deckard before him. When lorath remembers these nightmares he does so somewhat joyfully.
Personally I believe there is a secret campaign quest. I believe it starts in prologue. I believe it involves the prologue cellar and the prologue greed shrine and the prologue inarius statue before you go to kyovashad.
There are more variables to consider but there has to be something hidden within the prologue.
In prologue we have no access to stash so whatever it is can’t be too complex. It’s just complex enough people can’t do it on accident.
I think the defaced inarius statue is a coded message. When lorath rushes us to kyovashad I believe you are not suppose to rush to kyovashad at all.
I think the “rush to kyovashad” is the Diablo entering the portal to hell moment of Diablo 4. It’s widely known now that chasing Diablo into hell in Diablo 2 was a mistake.
Mephisto, Baal, and Diablo’s plan all hinged on us chasing Diablo into hell rather than trying to find Baal or Marius.
The more things change the more they stay the same. Why does lorath proudly carry the title of last horadrim as if he’s glad the order is gone.
Mephisto managed to corrupt every organized group of humans that existed. I think that’s a representation of the spread of hatred.
Mephisto is lorath nar. I am sure of it.