Board Thread:Episode Discussion Board/@comment-24675861-20151028034159/@comment-1895174-20151028061611

Maybe the entity possesses Will, and then they bring him (and "Death") back to Earth.

BOLD, WILDLY UNLIKELY THEORY: The planet is EGO, THE LIVING PLANET. Will described the planet in a way that makes it sound like it has some sort of sentience (what with it not wanting them to leave). Ego also has antibodies that attack intruders, and can create powerful, humanoid beings out of himself to attack other planets. Maybe the entity is one of those things.