Do you have link? As someone who's written 8bit platformers and effectively "copied" Mario's feel I didn't have to lower gravity to achieve a similar feel. I just set velocity while the button is held. There's no reason to lower gravity.

Mario is an 8bit game. There's no "real physics" in it. They aren't "applying a force to a mass". They're just adding an acceleration (gravity) to a velocity and that to a position.