Roko's basilisk: A thought experiment which states that an otherwise benevolent artificial superintelligence in the future would be incentivized to create a virtual reality simulation to torture anyone who knew of its potential existence but did not directly contribute to its advancement or development.

Many thousands of years ago, a group of twelve alien scientists was exiled to Earth. This group had created a machine that could cheat death—heresy, in the eyes of their leaders. Wounded and disoriented, they hid deep within its crust and separated themselves from the outside world while they got their bearings.

These scientists were kind, friendly people at first. They intended to make contact with the other intelligent lifeforms on the planet, perhaps integrate into their society. These lifeforms hadn't emerged yet, but they could wait—they were immortal, after all.

And yet, as years turned into decades, decades turned into centuries, and centuries turned into millenia...

Many of them became bitter. Angry. Vengeful. With nothing but time on their hands, they began to plot. They would gather support from the humans above them, give them the technology they needed to explore the stars... and then wage war on the planet that had abandoned them.

They chose to reveal themselves in the year 19XX. Which happened to be the year Gomez and Morticia Addams got married. Also, their original landing spot was in the same area as the Addams mansion, meaning that's where they'll emerge. Good luck, I guess?