Alr alr, so basically. The main character is a time traveler who goes back in time before he dies during a run to tell himself to run, causing a causation loop which makes the world fall apart because that isn't supposed to happen, the various entities are rotting long gone and corrupted past versions of himself.
All about how each entity works is in the description of the game, you can also turn on hitboxes in the settings by setting the opacity to 0.