After becoming a living computer virus, William Afton copied himself over and over again, taking over several factories that had recently installed smart technology and robots to automate the production lines.  Now, with near-unlimited resources and increasing supply of Remnant from specially made and melted capture animatronics, he's begun to build an army of killer animatronics to take over the world.

Now he has overrun the planet, and the last few humans have been either forced to possess animatronic bodies or been turned into horrifying Remnant zombies.  Some are still able to remember their past lives, and as such are more dangerous, capable of wielding various weapons including firearms.  The Nether is no better, with many having fled there and been slain by the zombie pigmen, who have taken their gear (most of it being military guns and armor).  But they aren't the worst things there.  The cybernetically-enhanced demons there are lethal monstrosities capable of melting through the best armor with enough time.

You must scavenge the world for anything you can find and manage to survive as long as possible.  New emerging technology, including powerful weapons, sustainable power generation and new methods of food/resource production will aid you in your survival, as well as plentiful defense options.  Stay on the move as a nomad, set up the ultimate fortress, build a secret network of tunnels between nearby structures, or gun it out in a small outpost.  The choice is yours.  Just don't let them get you, or it's all over.