An increasing number of animals classed as cryptids seem to be "one off" specimens, while one cannot, I feel, start considering that the world houses a breeding population of mothmen or batsquatches. Some have suggested they have been dropped off here by spacecraft. However, a possibility that we now have to consider, however fantastic it may seem to some, is that some of these creatures wander in and out of coexisting universes. The possibility that such universes exist has not yet been rejected totally by scientists, much less disproven. Narnia may lie behind the wardrobe door. The extra-dimensional notion was certainly considered by some of our ancestors and is receiving some scientific attention today from the likes of Michio Kaku and Colm Kelleher.
Incidentally, with regard to Mothman, there is a widespread idea that it was armless. One of the early witnesses, however, emphasised the fact that it had strong, muscular arms.