Board Thread:Questions and Answers/@comment-76.102.30.110-20130715013213/@comment-177.249.112.38-20150618180146

Yes I do agree that Skull Face being a hallucination is a better theory than the Gray Fox one, I think he is a hallucination and isn't at the same time.

What I belive is that Big Boss kills him at some point in the game, and as Big Boss descends into madness he begins to see hallucinations of Skull Face, also Psycho Mantis is preety much confirmed at this point, it has also been confirmed that the Specter in the hospital is an apparition of Volgin.

Maybe thats how Big Boss meets Psycho Mantis