So, as I mentioned in an earlier... ( I don't know the term. Post? Tumbl? Crack? Blog?), Superman only got his super powers after eating some of Ma Kent's baking.
For this prompt, the Kent's live in/around Coolville/Crystal Cove, and Clark became friends with the Scooby gang while growing up. Through a number of events, the Scooby gang receives powers, and forms the core of the justice league with Superman.
Shaggy is obviously a speedster, taking the place of the Flash. He can run real fast, and has to eat far more than a normal human can.
Scooby could be a Kryptonian super dog. If he is, then he belonged to Clark growing up, until Shaggy and Clark "married" and raised Scooby as their son. Eventually, Shaggy and Clark "divorced", and the judge (The school children) awards equal custody. (It was a highly controversial decision, and regular fist fights still break out even though none of the children are still in school)(Shaggy and Clark are best friends though)
Alternatively, Scooby could be able to transform into other animals, as well as be an excellent mimic. He could also turn into a larger version of himself.
Velma could be the girl in the chair. However, I propose something different. Hot Dog Water is the girl in the chair, and Velma is a cyborg-like character. Hell, both Hot Dog Water and Velma could have enhancements. They are also dating b/c obviously.
Daphne is Batman. Flat out. She funds the gang, knows a ridiculous amount of unique topics, and has a bit of a ditzy public persona. Either no additional powers, or maybe something that makes her really lucky.
Fred is difficult. On one hand, he could be Batman with how much he loves traps and in certain timelines is rich and acts like an absolute himbo. On the other, he is a bit of a himbo. So instead, he gets powers to control metal, somewhat.
Something that will let him tinker with the Mystery Machine, let him fully construct traps, let him lift large objects with ease. Eventually someone thinks to put some metal in a rope, and Fred now controls ropes. (The amount of sex/bondage jokes are outstanding, and Fred just smiles and nods along. He has no idea what anyone is talking about. People make a comment about kinks and he's just like "??? there are no kinks in this rope???". Fred is a human golden retriever.)
Scrappy could be a Bizzarro clone of Scooby, or just be part of a junior team.
The Hex girls absolutely get saved one time, and make custom theme songs for each of the gang as thanks.
Vincent Van Ghoul is like John Constantine. He uses his acting career as cover while he deals with demons. He is also unimpressed with the... lackadaisical attitude of the gang.
Ma and Pa Kent have that midwest farmer attitude. If you're there, you'll do your work and eat your fill. Family is the most important thing, and you leave 30 minutes to an hour after you say goodbye. You also leave with about twenty various leftovers. (Oh, we'll never eat this pie. And I know chocolate chip is your favorite. I made too much mashed potatoes, take some, etc.) They never throw anything away (It could be useful), and they always tell people to watch out for deer as they leave.
The Kents know Clark has super powers, so when he starts having helpers, they figure out who it is pretty quickly. Que Clark telling outrageous lies to protect his friends and his parents pretending to believe him. Ma Kent always piles Shaggy's food much higher than everyone b/c "he's a growing boy" and not because she knows he needs way more calories. Pa Kent asks for Fred's help around the farm because Fred can move tractors easier. Etc.
For the rest of the parents, they should be caring, but a little oblivious. except Fred's parents. Fred's parents being evil and him not realizing because he can be very oblivious to his loved ones is funny. Like, "Oh, my parents aren't evil, they just *insert terrible excuse that a five year old wouldn't fall for*"
I would say it could start 14-15 for that sweet, sweet puberty angst. and also to start the threats small. As the gang gets more used to their powers, they can start going further afield.
That's all I've got for now,
Tune in next time for more cracked out ideas.