Seems to be a pretty reasonable request. And the response from Jay Pavlina from Exploding Rabbit about the Super Mario Crossover source code was
So Jay Pavlina want's control over what he created, Super Mario Crossover. Makes sense, and that's actually why copyrights exist so that the creator is the only one with the right to copy what they created.
Jay Pavlina seems to have no issues taking that right away from Nintendo when he uses their assets in Super Mario Crossover.
That's all ladies and gents, what do you think?