I believed in pretty much the whole lot as a kid. When I was eleven my folks announced a weeks boating holiday in Scotland, including Loch Ness, and I threw a tantrum because I was scared of going to where the monster lives. I soon got over it. Loch Ness is one of my favourite places now.
UFOs as evidence of visitation by extraterrestrials I believed in whole heartedly, but as my reading showed how inconsistent reports were, I realised it was more likely to be a psychological phenomenon, as well as misidentification.
I used to take for granted that ghosts existed. Actually, outside of our cultural heritage, the evidence for ghosts is slim, and the chances of phenomena being interpreted through our cultural lense as ghosts seems high. More recently I've taken a more logical approach. I don't see a world about me in which humans have a separate personality which could survive death. I see one in which age, disease and damage can affect a person's brain, often changing their cognitive abilities and personalities.
I find cryptids endlessly fascinating, and once believed in every one. I'm sure great mysteries of nature still remain for us to discover, and there's nothing intrinsically impossible about many cryptids. But the process often used to interpret reports of cryptids weakens the discipline of cryptozoology. Looking for analogues in the fossil record, in spite of its known paucity, for example. When pointed out that the identity isn't a particularly good match, the cryptozoologists will often suggest that that is because of the tens of thousands, or millions, of years of evolution since. But then, the cryptid is as likely to be something not discovered in the fossil record. Anyway, while the odd cryptid may be a real creature, I'm sure that most aren't.
None of this is intended to dismiss phenomena. I'm sure the experiences people have are real in some ways, in some cases objectively, and they mean something, even if they're unlikely to mean what their usual interpretations suggest. Even if some supposed phenomena are known almost entirely from lies or hoaxes, that means something culturally. I've had a couple of experiences which have convinced me there is some kind of intelligence or intelligences existing in the wilder places, and perhaps sometimes nearer to our homes. Most would have interpreted them as ghosts, but I see no such evidence. I sometimes half joke that I believe in fairies, but that's neither especially accurate nor too far from the truth. I just believe in something I don't have an explanation for.
This post is too long so I'm done for now