I've had a fascination with this subject since I was young. One could often find me in the school library as a youngster in the UFO / bigfoot section.
I've always perceived that there is more to this world that we inhabit than our 5 senses can decipher. When I was a child it was easier to perceive such concepts although I was often frightened by them.
Since my awakening of late, my interest in these subjects has returned. Of course I can't say with any certainty, but here is my current understanding/guess:
As far as cryptids are concerned, from what I'm learning, I really do think that physical creatures have the ability to "evolve" or mutate to a large degree depending on environmental factors.
It's evident by the specific biodiversity of individual regions of the planet that the species dwelling there seem to specifically "fit" that particular area, as if they were meant to be there. The continent of Australia is a good example. I would go as far as to say that the humans dwelling in that region have also evolved physically to be most efficient for that specific environment. I'm speaking of the aboriginal "first nations" peoples.
Mountain goats and sheep in the rocky mountain region are similar but different to the species in Europe or Asia. But they are all sheep and goats (a kind) and well adapted to their specific region. Were they specifically created that way or was there one basic original prototype set in place and what we see today and throughout the paleolithic record are simply mutations/evolved to adapt to the ever changing environment?
Personally I have to think that they evolved to adapt. This leads me to believe that species can also appear and disappear depending on the current environmental factors. Maybe there are rare species from an older age still lingering to an extent or new species now evolving to a new age/environment.
One example is the thylacine or Tasmanian tiger. It is thought to be extinct but there have been many recent sightings of this animal. Perhaps It can is in a transition phase - On it's way out but another predatory creature will take its place to create a balance.
Thylacine, the largest carnivorous marsupial of recent times, presumed extinct soon after the last captive individual died in 1936.
www.britannica.com
There are likely other survivors of a bygone age that are rarely seen. I don't think that the creator formed each individual creature as we see them today. He built in the capacity to adapt and that mechanism has great potential. There are forces beyond our limited knowledge that shape and influence the world around us.
For the record, I'm not claiming evolution between species (primate to homosapien) but rather a broad ability to adapt within a species "kind".
There is a theory that is very plausible which postulates the idea of a vapor canopy enveloping the earth before the time of the flood. The Bible account alludes to this possibility. This condition created and entirely different environment to the one we are used to. The canopy blocked the suns UV and other radiation to a large extent. This enabled a great transformation of Earthly species, giving rise to giants and Titans both in the animal and human kinds (human men of fame) with vastly superior abilities. This enabled them to dominate. The Greek and Roman mythology of the titans was likely speaking of such ones. Perhaps this is also what gave rise to the stories of the Biblical Nephilim. These stories have counterparts in many ancient cultures.
I realize that this thought is not congruent with those who take a literal view of the Bible but I'm beginning to open up to other possibilities. This would explain the ages of the dinosaurs, etc.
So much of ancient history has been hidden.
The rabbit hole goes much deeper but it's probably too much for this forum so I'll leave it there for now.