Courage the cowardly dog
The monsters that Courage sees are just people from a dog's perspective.
Courage is actually a normal dog and he sees the world through a dog's eyes. All the villains in the show are just normal people, but to a little dog they seem scary. They don't actually live in the middle of Nowhere, but since his owners are too old to take him outside for walks, he only knows what's around his immediate property, and everything beyond that is nothing because he's never seen it. Also explains why Courage always feels like he has to "protect" his owners from all the scary things, even though the owners are very nonchalant about all of the situations, and act like everything is normal and Courage is freaking out for apparently no reason.
Source- Smosh.com
My opinion- wow this explains so much!