If you enter the Konami Code before you enter the 4th pipe, you enter a Secret area. it's an underground 5-2.
Picked up Mushroom in 1-3. Picked up Fire Flower in 2-1. Didn't die. BEST AND HARD GAME TO SPEEDRUN!!!!!!
Died from goomba (or face slapped on goomba) on first attempt at 8-4, truly a nightmarish game to speedrun.