In this fanfiction, I will be using information Edward Kay has confirmed (in both his original and current concept) to construct what I think the origins are. But some of this stuff is also just wild mass guessing.
The portal to Miseryvile is a well. This isn't confirmed by any of the creators, just a concept I made up. And I am keeping it until I find out whether or not Pomegranate and Herman return to earth when they leave Miseryvile. I originally was thinking Jimmy jumped into the well to hide from a Mary Sue like character, but Jimmy isn't that shallow. So instead, I will say Jimmy fell in by accident. Jimmy had the opportunity to return to earth, but that's for another story. When Lucius found out about Jimmy, he hired a zombie like Heloise to make him miserable. She tried many things such as electrocuting him, blowing him up in a boat, and tying him to a rocket. But no matter what she did, Jimmy didn't mind. No one has ever been this kind to Heloise before, especially not after trying to torture them. And at that moment some people say, Heloise's heart-you know the rest. Heloise changed from her zombie form to the one we know her for today. She then offered Jimmy to live in an abandoned house between Heloise's and Beezy's. While it's not hard for me to believe Jimmy met Beezy before Heloise, Beezy didn't get a concept art until later.