Remember: Hamlet and the ghost interact, so this will take away several options when you think of the logistics. For example, can the actor change make-up and costume within a given scene? Probably not. Second, think of what is noticeable on stage as for as presence, especially considering the Elizabethan theatre that Hamlet was originally written to be performed in. One answer will clearly stand out if you think of yourself as someone watching and listening to the play.
