Weird Fan fic idea

[Mr. Marshmallow]

I've been thinking about this a while now and I think this would be a great idea for a fan fic. What if someone came to Foster's but was NOT an imaginary friend and not a human dressed in drag (ala Goofball)?

I mean consider this: Foster's is filled with dragons, giant hairy purpled horned monsters, bird plane plant things, slime creatures and giant talking rabbits. If a REAL monster or creature or something like that showed up, how would you know the difference?

I was thinking this creature could show up at Foster's and Frankie and Mac and the others welcome the creature in, but when they talk to him, he doesn't seem able to understand the whole concept of imaginary friend and creator like that.

The idea is that how would you know if this thing isn't a real LIVE monster and not an imaginary friend? How could you tell the difference? What do you think?