The antagonist is a mysterious place more so than a person. More specifically it’s an island so I think three words to describe it would be, mysteries, uncaring, and magical.

I know this is not a personality as places are inanimate but no one really knows anything about this island and there is no maps of it making it a mysterious place.

Being an island means that it does not care if you live or die. It is not going to help you accomplish your mission or goals. It will kill you with out any concern about anyone else.

Any island that does not stay in one place is clearly magical in one way or another. No one knows about the magic the island holds making it harder to figure out how to get back to reality once they are on the island.