All of it is a load of hooooiiiieeeeee! IMO! No offense to anyone, just what I believe.
Bigfoot and Nessie --- those I think in theory could be possible. Look in the last 2 years all the new discoveries that have been made of animal species. Now granted, they are frog and fish size, not larger than man or dinosaur size. But over all I think that we would have had more evidence by now if they did exist and that film of bigfoot was faked, it was admitted to.
Ghosts/spirits --- nope, as someone above said, it would be sad to think that this life was all there was and there wasn't an afterlife....well, it would be even sadder to think that now you are some disembodied spirit, floating around flicking lights on and off and making noises in someone's house. (although, now that I think about it, that could be fun!) Actually, I believe what it says in the Bible that it is appointed once for man to die and after that comes the judgement. We are told to be absent from the body is to be present with the Lord, so there is no room for ghosts or spirits.
Aliens and UFOs -- no, God made mankind in his image and made him unique. Don't think there is life on other planets however some Christians might disagree and I wouldn't argue (much) with them because it is one of those things that unless you are there, you can't prove one way or another. (but after seeing the Astronaught Farmer, I have started building my own rocket so I'll let you know in a couple of years.)
IMO--- remember that before you start to flame me ---- IMO, I feel that this stuff is mainly people's imaginations, fear that feeds our imaginations and easily spreads, governmental activities that have been covered up (cold war situations ---- plus I don't buy into alot of the conspiracy theories although I believe that there could be truth behind many of them), and just people misinterrupting situations around them. Also, as far as the truly unexplained things that may go on, I would attribute some of that to demonic activities, which would account for the true hauntings.
Again, all of this----IMO (although I am right...

j/k )