Ghost

Ghosts are "entities" implied to exist by Bob (mod creator). Every 3 meters (presumably in every possible direction), there is a ghost. They are neither visible nor capable of interacting with anything in any sense. By all practical and realistic means, they essentially do not exist. Whether or not this is some sort of thought experiment or a strange joke cannot be confirmed. They have no explanation or lore beyond that they supposedly exist and don't exist at the same time.

These "ghosts" would be impossible to prove that they exist, since they are completely undetectable by all means, however, they are also impossible to disprove for the exact same reason. Though, one could state that, within the confines of the context of the world (or the game's), they don't exist, since they will never interact with the world or have any impact on its course in time regardless. However, it has made an impact on the world, in some way, just with the mere idea or concept of them. Simply by having the idea in your mind, these "ghosts" that are not supposed to be able to interact with the world or make any change, have, as your actions are changed because of it, not matter how minuscule. To call to the Butterfly Effect, even the tiniest and undetectable of differences, over time, can grow to a massive scale. Who knows what could've changed, just with the mere concept of these "ghosts", given enough time. Unless you actively try you best as to not spread this idea, in which case it still causes change in the world due to your efforts, it will spread to others, who will be changed, and to more, like a virus. More accurately perhaps, a meme, the DNA of the soul. At this point, it no longer matters if these "ghosts" exist or not, since the very idea of them has made them real, in one way or another.