The trek to California is accomplished primarily by gambling — a series of double-your-money hustles instigated by the queerly parentless Haley. We actually get to see Haley’s trailer home at one point, though her father (a trucker) is on the road. In addition to video game-related hustles, the trio end up at one point in an actual casino, wherein Haley’s skill at craps allows an adult (“Spankey,” a mentally challenged “trucker friend” of her father’s, played by Frank McRae) to win hundreds. It’s later revealed that Haley’s deceased mother had a gambling problem, which apparently led to Haley’s hustling skills. Corey’s mother is also dead. And Jimmy’s sister/Corey’s half-sister? She’s dead, too. What?! Never mind that now. We have to get to California.
The climax involves a video game tournament, so you can guess the ending. It doesn't make any sense, either. Read more about how a favorite movie from a writer's childhood becomes completely nonsensical when he watches it again as an adult. Link
Also, if you haven't heard of them, you need to check out little monsters and the monster squad. Two other awfully good 80s movies.
Then the family reunites and reconciles and solves all their problems. It was sort of like Rainman, but with kids and video games
There's a heavy nostalgia factor for my age group with this for sure, but that's how big Super Mario Brothers was in our lives: It didn't even come CLOSE to seeming weird that a movie would climax with the revelation of Super Mario Brothers 3.