Most of those discovered so far don't amount to much outside a fun diversion from the usual outlaw activities, but a brand new easter egg that was found recently seems to hint at future content coming to the game.
Before we proceed further, there are some huge end-game spoilers below this point. Avoid reading at all costs if you haven't reached the Epilogue and don't want to ruin one of the game's big twists.
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After completing Chapter 6, players will no longer control Arthur Morgan, but the beloved Red Dead Redemption protagonist John Marston. You will also be brought back to the New Austin area to complete the game's final missions.
To experience this new Easter Egg, you need to head to the Tall Trees region on the map and jump down a well. Here, the character will start glowing in the dark and will become zombified in a form that is not too different from the one seen on the Undead Nightmare cover. The same can happen if you somehow manage to get Arthur down this well, but the effects are not as pronounced. You can see a video of the Easter Egg in action here.
This new zombie-themed Easter Egg may be a simple diversion added for fun to the game by Rockstar Games, but its location seems to suggest that there could be something more behind it.
Rockstar has yet to reveal any plans for single-player DLC expansions, and we probably won't hear anything for quite some time (if at all) considering that Red Dead Online is literally launching as we speak in beta and that it will of course require additional work before its official launch.
The original Red Dead Redemption Undead Nightmare DLC expansion was released a few months after the main game launched on PlayStation 3 and Xbox 360 and is completely standalone, meaning that it can be played even without owning Red Dead Redemption. The expansion features a zombie-themed horror campaign, starring John Marston once again as he searches New Austin for the cure of a plague that's infesting the area. During the course of the campaign, John meets many of the characters he encountered during his first journey, but they are somewhat different to fit the theme of the expansion.
The Undead Nightmare expansion campaign doesn't play too differently from the main Red Dead Redemption campaign, with players controlling John in a big open-world setting completing missions given by various NPCs. Side missions given by Strangers as well as Chance Encounters are also available, and all have been modified slightly to fit into the expansion. The Undead Nightmare expansion also adds two new multiplayer modes and several cosmetic additions.
Now that the zombie-themed Easter Egg in Red Dead Redemption 2 has been discovered, Rockstar Games may surprise us in the future and officially announce Undead Nightmare 2. We will let you know more about this possible expansion as soon as possible, so stay tuned for all the latest news.