Every cat is a monster of one kind or another, but most cat owners don’t think of their cats as literal monsters (even though they can be destructive). Yet over the centuries that people and cats have lived together, it’s only natural that people would see cats as evil because of their self-centered behavior. That’s probably why so many mythological creatures are based on cats.
Such cat monsters exhibit traits commonly associated with ordinary house cats. For example, the cactus cat supposedly was a desert predator. To avoid the harsh heat, they’d carve out the inside of a cactus and sleep through the day. It eats the bugs and juice of the cactus, keeping it hydrated.