UFO Sighting
Like in Grand Theft Auto 5 which is another game from Rockstar Games, they added a UFO sighting easter egg in Red Dead Redemption 2. You can spot the UFO two times. To make the UFO appear, look for Hani's Bethel, an abandoned shack filled with dead cultists by a small lake located in New Hanover, east of Valentine just north of Emerald Station. If you pick an old letter at the desk at the center of the room, it is read as follows:
Mysterious Sermon
At the second hour under the half moon
By the great love and grace of our savior Kuhkowaba
Voyager of the time and galaxies
We cast off our corporal shells
So his vessel can take our spirits to the promised realm
To live in peace and power until the two thousandth year
When we will return for the new chosen
And worship once again at the peak of mount Shann
In his love we rejoice always
If you head over to this location (or return here after reading the letter) around 2 AM in game time and with half moon in the sky, you'll notice that the surroundings will be lit green and you'll find the UFO above the shack, flying off.
Now head over to Mt. Shann located in Big Valley, north of Strawberry, just above the Hawks Eye Creek and look for a rock circle at the top of the mountain. Make sure it is a half moon and time is around 2am in-game. After walking over the rock circle, you'll find the UFO the second time, floating from afar. You might need binoculars to see the UFO clearly.
It is believed that this easter egg is a reference to Heaven's Gate, a UFO religious cult founded on 1974 consisting of around 40 members who committed mass suicide in order to what they believe is to aboard a spacecraft that was trailing the comet Hale-Bopp.
Also, if you explore Hani's Bethel, you can also get an Aged Pirate Rum under the chimney which will give a good chunk of boost to Arthur's stamina as well Dr. Hawthorne's collectible cigarette card on a desk between the beds on the right.
Viking Tomb
You can find this easter egg north of Annesburg near Roanoke Valley (just below the letter R on the map). It is the star-shaped area on that part of the map where you'll come across a Viking burial tomb.
Here you'll find a Viking Hatchet which you can use as a throwable weapon. If you explore further down there is a cave where inside you can find a Viking Helmet which you can wear as a hat. You can actually get some different interesting dialogues from certain NPCs while wearing the Viking Helmet.
Well Prisoner
At the north of Eris Field near Compson's Stead, in between the letters E and M of Lemoyne on the map, you'll see a locked house with a well on the front. There is a ladder inside the well that you can descend into and upon inspecting, you can pick up $0.25 coins scattered around and on the wall of the well you can see carvings that suggest that there was a prisoner in here before who counted 62 days (as implied by the 62 marks on the wall) before he was freed using the ladder that you used to descend to it. Under that there are carvings of 3 clouds, 3 crosses, and a sun.
Whispers In The Forest
Another ghostly easter egg can be found in a forest in Roanoke Valley, north of Annesburg and just a bit south of Brandywine Drop. Once you arrive in this area at night, you'll hear two creepy voices, apparently from a boy and a girl, whispering back and forth. The dialogue are as follows:
Girl: "What's that terrible noise?"
Boy: "Must be a sick calf looking for its momma, they've been known to bawl like that." (laughter)
Girl: "You should be ashamed of yourself, Eugene Hutton.
"I need to get back home. I need to get back home!"
The voices belong to a young couple from Annesburg named Ethel Boshared and Eugene Hutton. If you watch in some theaters in the game, you can watch a show titled "The Ghastly Serenade" which narrates the sad story of the young couple.
While courting each other in that same forest, they got lost and stumbled upon what seems to be a dead army of British soldiers. Eugene's head was cut off the by the ghostly soldiers, and Ethel, running in fright, returned home with Eugene's head in her hands. When she told the story to the villagers, nobody believed her and instead accused her of witchcraft and burned her alive on a stake.
Witches Cauldron
You can find a small shack just a bit above the letter N in Ambarino on the map. Once there, you can loot a chest containing Hair Tonic and Snake Oil. You can also find a cauldron containing a some kind of boiling black liquid. Taking a sip of the mysterious liquid will make Arthur pass out and he'll wake up a few meters away from the shack. There are no known effects of the mysterious liquid to Arthur's health, stamina, inventory or anything whatsoever.
