On this week's of my ideas of Cryptozoologicon!
Goblins and Gremlins: Troglodyte bat-like primates with pale luminescent skin and live usually in caves. Goblins and gremlins are eusocial beings and dwell on the surface at night. In the early days, certain evolutionary offshoots of hominids dwelled deeper into caves and adapted to the surroundings due to high evolutionary pressure. They adapted sonar, climbing extremities, pointed ears, and pale slime bodies. Eventually, they even formed a symbiosis with lumicient bacteria. They prey for fish, small animals, and prey falling into caves by accidents and at night will sneak out and stalk the woods sometimes breaking into human households to steal goods.
I'm also thinking of making ogres and trolls carnivorous great apes. It's the only logical explanation I can think of them if they were real animals.