A lot of the easter eggs in Halo 3 I personally find a little unsettling.
The Cavemen are just these weird human things that bleed when you shoot them but appear to be petrified with their eyes just lifeless and staring at nothing.
There’s that bouncing image of some dev in boxers at the beginning of the last level that is tucked away in a dark corner just quietly bouncing up and down without making a single sound. Plus another similar image in some DLC multiplayer map.
There’s the whole “Trigate Mystery” thing which I know fuckall about despite how many videos I’ve seen on it, plus that weird looking texture in some wall way out of bounds in The Ark level. And going out of bounds in general can be a little unsettling since the world just gets more and more distorted and abstract (obviously since you’re not supposed to be there in the first place) kinda like the “Blue Hell” areas in GTA San Andreas.
And then of course there’s the mythical “ghosts” in the multiplayer. I remember spending hours watching all kinds of supposed ghosts on youtube. From the iconic ghost player that would glide around the map with broken movement animations and attack players to grenades and equipment being thrown around by a second player in what is supposed to be a solo lobby. Even though all these supposed ghosts could be dismissed as players just skillfully recording and editing footage to make it look real.
Not exactly Silent Hill or Amnesia, but there were a few things about this game that were just a bit unsettling.