I was in a world and a got off in a village, when I came back on Minecraft the world picture was covered with Alex faces but white eyes, also me and my friend keep seeing a black player looking entity that appears in the mountains on both our realms.

EDIT: The black entity sets fire on everything around it when it disappears. With no flint and steel in its hand. We think it is a corrupted AI from when the Minecraft testing was made.