The dark steve is a Virus that appears when someone plays with the Default Steve Skin 10,000 times in a row. When he spawns, blocks suddenly disappear and Villages and Villagers go missing.
He stalks around your world and when he finds you, he will chase you until the end of time. Then he will start punching you. A single punch can remove a game on your device.
There is one way to get rid of The dark steve. Once he has removed five of your games, you leave the world and delete it. If you do that before he has removed five of your games, he will still be on your world.
If you get rid of him, he can come back, but the amount of Steves you play as doubles every time. e.g: 20,000 then 40,000 then 80,000 then 160,000 e.t.c.