The Babadook: The Babadook itself IS real, but its a manifestation of Amelia's magic/power. The Babadook is typically accepted as a story about dealing with Grief and Trauma. The Babadook itself is often taken as metaphorical. Its all in Amelia's mind, as it were.

The Babadook's ending serves as a metaphor for accepting and living with one's inner demons, particularly depression, rather than trying to banish them.