Hypothetical - Multiplayer Horror

[Ghieri]

For example you could use the fog, darkness and graphics style to make
other players almost indistinguishable from enemies. So sometimes you'd
see some strange thing scurrying away from you, sometimes you're
unknowingly hiding from another player who's just as puzzled as you were
before... of course there's the danger that players would try to find a
way to signal each other so communication would need to be entirely
removed. Also you could leave players in the dark about what their
character looks like, so they don't know how they'd even identify
another player... still, I guess it would probably be noticeable because
players move differently than AI driven characters...

Or you could literally make other players untrustworthy. Like in LoZ four sword, all players have one goal, but at the same time, they can compete for resources(And even damage other players.) and there's a final score showing who the better player is.