Poppa Henry's Ghost[]
At the beginning of the movie, Arlo's father, Henry, was killed due to the storm nearby their home. Before this happens, he wanted to see his children "earn their mark", and while he did see Buck and Libby get theirs, he had yet to see Arlo earn his. This forbade him for passing on into the afterlife, looming as a ghost close to where he died.
Eventually, Arlo ended up returning to the similar area, being pushed off a Cliffside by Thunderclap's clan, passed out. Here, Henry returns to Arlo, and almost brings him into the afterlife with him after he gets knocked out. This would explain why he never stopped to help Arlo, and kept him moving despite Arlo's plee. When Arlo explains why he can't go with him, Henry finally saw him earn his mark in the world, and finally was able to put his own soul to rest, passing on to heaven.