by TheLionPrince » February 3rd, 2017, 7:06 pm
Well, that's an awful theory. Several characters besides Simba have interacted with him and seen him. Adding onto Elton's statement, even Timon, Pumbaa, and Nala noticed his presence, and the latter even responded to his statement that Simba had returned.
Like Panda-chan stated, the theory is that Mufasa's ghost was a hallucination. However, the theory has been denied by the filmmakers on the audio commentary when they refer to it repeatedly as "Mufasa's ghost".