just also watched the film THE WARD where a multiple personalities lead actresses was plagued by ä "vengeful ghost" which gradually killed all her split characters. but that is another category of external being manifestation which could be the person's crazy imagination doing havocs to his life or really a manifestation of an external being.
another show i watched depicted a young boy who was born with the ability to "astro travel" i.e., his soul leaving his body and wandered off to a cosmic plane. while his soul was away, his empty body shell was at the mercy of other lost sprits which were trying to possess it.
External being could be malevolent or benevolent depending which origins it's from. if it's fr the light, it should be benevolent while those fr the darkside should be the treacherous evil one.