Writing : When have you crossed the line into copyright infringement?

Inspiration recently kicked me in the head for a great SS idea. I'm not particularly worried about people up and stealing it, cause they'd likely hit the same copyright/trademark issues I would, so here it goes:

I was listening to Isis (The metal band) on my Android and I saw a poster for some old Super Mario game. In about five seconds I had reimagined the entire first Super Mario Brother's game through a bizarro/horror lens of Gritty Italian sterotypes from the early forties, a Femme Fatale, living bloated Fungus, derelict castles, steroidal botany, a several stories tall monster with a shell of rotting barnacles, and a whole host of other twists.

Then I laughed at myself for even thinking about it since I could never disguise that it's essentially Super Mario Brothers, especially since the fun of it would be that everybody would know that it is Super Mario Bros on bad acid, at least that would be the goal.

I could very well write it just for kicks, but it got me thinking. How far must you distance yourself from your original insipration in order for it to be original enough to publish? They say you can't copyright an idea and Satire gives nearly unlimited license, but is everything outside of that simply a judgment call on the part of the editor you've submitted to? I know its been discussed on the forum before, but I figured this could be a an interesting excercise to see how to address this issue without people being gaurded that someone is going to steal their idea.

If you had a dour, gritty, dirt-under-the-nails plumber from Bay Ridge lost in a Lovecraftian mushroom kingdom, would you have to change the color of his overalls? Make him wear pants? Make him an electrician? Or could you simply keep almost everything the same but change the name from Mario to Vinnie?