It is a bit of a wide ranging question isn't it ? Tying together ghosts, UFOs the unexplained and god.
If by ghosts you are referring to folk discovering they continue to exist in some form after their body has died, then I believe I have had quite a bit of evidence for that. I suspect most of those who refuse to believe probably haven't looked.
There are things that fly, some of which don't get identified, so by definition there are such things as UFOs. If you mean aliens visiting from elsewhere in the universe, I think the evidence is too skimpy at the moment, but it is not outside the realm of possibility. The universe is vast so the chances of intelligent life elsewhere should be good. Whether they develop the ability to come here or even to find us, is another matter.
"Unexplained" is far too vague to comment on.
IMO God is the name we put to the first cause of everything. Unless you are going to believe there was no first cause, then God must exist in some form or other.
Ghosts or indeed anything else may not have a reason. What is the reason for us being here ? It is possible there isn't one even though we might want there to be, and might find lots of justifications; reason implies intent, which may not be there.