Originally posted by Cursed Lightslei
That would be fine in a level that goes from right to left though I assume, right?
No, actually. The sprite has been setup so that if you clear the extra bit, Mario will go left instead of right. If you changed that value from a positive to negative number he would continue to face right but would run backwards. If you want to change the speed of Mario going left you would have to change the value on line 54 to something greater (more negative) than $F0. The RAM map gives more of an explanation on those addresses if you're curious.
I apologize if this is going astray from the original topic.