This is getting very interesting, as second UFO is spotted in the game on Mount Shann and this time is a different color than the first one.
The very first UFO was green color and has been seen north of Emerald Ranch. There was a hidden message with instructions to follow – return to the cabin near the lake at 2:00 AM on a night with a Half Moon.
When we visited the cabin again, a green light showed up in the sky and a green UFO was seen.
The letter that we found mentioned Mount Shann, but at that point, we had no idea what Mount Shann is or where can be found, until today.
We found Mount Shann, went to the location shown in the image below at 2:00 AM and saw the second, red UFO.
Here is the second UFO spotted in Red Dead Redemption 2.