Tip: Make sure that ALL exit-enabled pipes, doors, etc. have a screen exit defined, or they'll take you to Level 0, the "endless" bonus game. Unless Start+Select is enabled, the only way out of it is to reset the game.
I have seen codes made to change Mario's powerup status at the beginning of the game. However, I have noticed that there has not been anything posted that talks about including player 2 with that. I haven't been able to figure it out. Is there a way to start player 1 AND player 2 Big just at the beginning of the game?