Before you can even begin to say that a certain crypted exists you have to examine the evidence and determine if such a creature can exist. I have devised several questions that I asked myself about such creatures before I put forth any effort to believe them. If the answer is 'no' to any of the following questions then said creature probably doesn't exist. But just because you can answer yes to all the questions only allows for the possibility for the creature to exist. I doesn't prove it does.
Can the creature exist without violating the laws of physics or biology?
A couple of examples of this are Batsquatch and the famous chupacabra. Batsquatch, a large Bigfoot like animals that flies around with big bat like wings. Violates the laws of physics, doesn't exist. Chupacabra, a crypted that lives only on the blood of goats. Blood alone doesn't contain enough nutrients to sustain a creature of its reported size. Violates the laws of biology, doesn't exist.
Where the two most well-known crypteds, Bigfoot and the lochness monster on this question are like this. Bigfoot is really only a big ass hairy monkey which doesn't violate any natural laws. Loch Ness Monster, such creatures have existed in the prehistoric past. No reason they can'y exist today.
Is there credible circumstantial evidence for the creature to exist? Are there credible eyewitnesses, footprints, credible photos, and or remains?
In the case of batsquatch? Really? How many of you have ever heard of batsquatch before this posting? In the case of the chupacabra, there lots of witnesses that saw something, most don't agree on the same animal. There is evidence of attacks on farm animals but most of those can written off as known animals. There is even a short film of what looks like a shaved dog to me running.
In the case of Bigfoot there reliable witnesses, foot prints, some film stock that can't be completely ruled out. There is other body prints and 1 or 2 large piles of shit. If Bigfoot was a murder trial based on circumstantial evidence along we would have had a hanging a long time ago.
In the case of the lochness monster, there is some witnesses and pictures, of something. Most of which can be explained by perfectly natural creatures or events.
Is there a entry in the fossil record for a creature similar or related to said cryptid?
In the case of batsquatch and the chupacabra, no there isn't any such records.
In the case of Bigfoot we have Gigantopithecus. In the case of Nessie, we have the Plesiosaurus.
Can the creatures reported habitat sustain a large enough population while keeping it mostly hidden.
Batsquatch, nobody knows the real habitat of this cryptid. It has been seen only a few times in a very small area. Chubracabra, well there are lots of goats out there to suck on, so who knows.
As for lochness, well while the loch is big, it isn't big enough to sustain a large enough breeding population of creatures this size. The loch is also poor in nutrients so it probably can't sustain even a small number of creatures. Sorry, Nessie but you probably don't exist.
Only in the case of Bigfoot is all the requirements of this question positive. Most cases and sightings are in the North American North West. There is millions of square miles to hide and sustain colonies of these creatures. There is large stocks of fish and other game if they are meat eaters. If they are not, there is plenty of grasses, plants, and roots too.
While this doesn't prove that there is a large unknown hairy ape roaming the country. It certainly does allow for the possibility.